THE EFFECTS OF SPOTTED KNAPWEED (Centaurea stoebe L.) ON GRASSLAND
PLANTS AND SOILS IN BRITISH COLUMBIA

By
YUYING KUANG
Bachelor of Science in Environmental Sciences, South China Agricultural University, 2010
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF
MASTER OF SCIENCE IN ENVIRONMENTAL SCIENCES
in the Faculty of Science

Thesis examining committee:
Lauchlan Fraser (Ph.D.), Professor and Thesis Supervisor, Department of Natural Resource
Sciences, Department of Biological Sciences, Thompson Rivers University
Wendy Gardner (Ph.D.), Associate Professor and Committee Member, Department of
Natural Resource Sciences, Thompson Rivers University
Cynthia Ross Friedman (Ph.D.), Professor and Committee Member, Department of
Biological Sciences, Thompson Rivers University
Mila Kwiatkowska (Ph.D.), Associate Professor and Committee Member, Department of
Computing Science, Thompson Rivers University
David Clements (Ph. D.), Professor and External Examiner, Department of Biology and
Environmental Studies, Trinity Western University

August 2015
Thompson Rivers University
© Yuying Kuang, 2015
Thesis Supervisor: Professor Lauchlan Fraser

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ABSTRACT
In British Columbia, grasslands provide critical habitat for a wide variety of species
and are a significant forage base for BC’s ranching industry. Grasslands in BC are threatened
from several human-caused stressors, including urban development, over-grazing, climate
change and the introduction of non-native invasive species. Spotted knapweed (Centaurea
stoebe L.), is an invasive plant introduced to North America from Europe. It can establish
large monocultures in BC’s grasslands which can cause a reduction in wildlife and livestock
forage production, a lowering of native biodiversity, and an alteration in soil nutrient
composition. I investigated the carry over effects immediately following removal of large
and small spotted knapweed patches on soil mineral nutrients (nitrogen (N), phosphorus (P),
carbon (C) and volumetric water content) and the growth of an important native grass, rough
fescue (Festuca campestris Rydb.), in grasslands within Lac du Bois Provincial Park, located
to the northwest of the city of Kamloops, British Columbia. The results of field experiments
showed that soil total nitrogen, total carbon, volumetric water content and biomass of rough
fescue were lower in former spotted knapweed patches, but there was no significant
difference in soil total phosphorus. In addition, there was no measureable difference between
large and small spotted knapweed patches in soil mineral nutrients and plant growth. In a
greenhouse experiment I manipulated N:P ratios (1:1, 15:1 and 30:1) and biochar (10g/pot or
none) to test their effect on competitive performance between spotted knapweed and rough
fescue. The experimental design included five plant combinations: spotted knapweed alone,
rough fescue alone, two spotted knapweed, two rough fescue, one spotted knapweed and one
rough fescue. The results of the greenhouse experiment showed that total biomass of spotted
knapweed was greater than rough fescue at each N:P ratio when they were grown alone or
grown under intraspecific condition. Also, results showed that the competitive effect of
spotted knapweed was -0.136 ± 0.052 SE; while rough fescue has a facilitation effect of
0.020 ± 0.007 SE. Biochar addition had no effect on plant growth of spotted knapweed or
rough fescue, or competitive interactions within and between the two plant species.

Keywords: Soil properties, biomass, carryover effects, N:P ratio, biochar addition

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TABLE OF CONTENTS
ABSTRACT ............................................................................................................................. ii
TABLE OF CONTENTS ...................................................................................................... iii
ACKNOWLEDGEMENT ..................................................................................................... vi
LIST OF FIGURES .............................................................................................................. vii
LIST OF TABLES ............................................................................................................... viii
CHAPTER 1 ˗ GENERAL INTRODUCTION .....................................................................1
Grasslands ............................................................................................................................... 1
Spotted knapweed (Centaurea stoebe L.) .............................................................................. 2
Rough fescue (Festuca campestris Rydb.) ............................................................................. 3
Competition and soil nutrients .............................................................................................. 4
Biochar ..................................................................................................................................... 5
Thesis Research Objectives .................................................................................................... 5
References ................................................................................................................................ 6
CHAPTER 2 ˗ SOIL RESIDUAL EFFECTS OF SPOTTED KNAPWEED ON SOIL
PROPERTIES AND VEGETATION AT LAC DU BIOS GRASSLANDS
PROVINCIAL PARK .............................................................................................................9
Introduction ............................................................................................................................. 9
Materials and Methods ......................................................................................................... 11
Site description .................................................................................................................... 11
Experimental design ............................................................................................................ 11
Sampling, Measurements and Analysis .............................................................................. 12
Statistical Analysis .............................................................................................................. 13
Results .................................................................................................................................... 13
Discussion............................................................................................................................... 15

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Soil nitrogen ........................................................................................................................ 15
Soil carbon........................................................................................................................... 16
Soil phosphorus ................................................................................................................... 16
Soil volumetric water content ............................................................................................. 17
Biomass ............................................................................................................................... 17
Differences between large and small patches ..................................................................... 18
Linear regression ................................................................................................................. 18
References .............................................................................................................................. 19
CHAPTER 3 ˗ COMPETITIVE EFFECTS FROM SPOTTED KNAPWEED ON
ROUGH FESCUE WITH OR WITHOUT BIOCHAR ADDITION AT DIFFERENT N:
P RATIOS ...............................................................................................................................23
Introduction ........................................................................................................................... 23
Competition ......................................................................................................................... 23
N:P ratio .............................................................................................................................. 24
Biochar ................................................................................................................................ 24
Materials and Methods ......................................................................................................... 26
Experimental design ............................................................................................................ 26
Species ................................................................................................................................. 26
Greenhouse conditions ........................................................................................................ 26
Germination ......................................................................................................................... 27
Treatments ........................................................................................................................... 27
Harvesting ........................................................................................................................... 29
Statistical analysis ............................................................................................................... 29
Results .................................................................................................................................... 30
Total biomass ...................................................................................................................... 30
Competitive importance ...................................................................................................... 34
Discussion............................................................................................................................... 37
Total biomass ...................................................................................................................... 37
Competitive importance ...................................................................................................... 38
References .............................................................................................................................. 40
CHAPTER 4 – GENERAL CONCLUSIONS, MANAGEMENT IMPLICATIONS AND
DIRECTIONS FOR FUTURE RESEARCH ......................................................................43
Conclusion ............................................................................................................................. 43
Management implications .................................................................................................... 44

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Future research directions ................................................................................................... 44
References .............................................................................................................................. 46
APPENDIX A .........................................................................................................................47
APPENDIX B .........................................................................................................................61

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ACKNOWLEDGEMENT
Financial support from Natural Sciences and Engineering Research Council of
Canada.
I sincerely thank my supervisor Dr. Lauchlan Fraser, who guided me from the
beginning. Since I first arrived at Thompson Rivers University, confusion came around. I had
no idea how or what I should do. Fortunately, Lauchlan patiently guided me. He led me to
the right track of study and life in this strange place. Many thanks to members of my
committee: Dr. Wendy Gardner, Dr. Mila Kwiatkowska and Dr. Cynthia Ross Friedman.
Thanks to Kathy Baethke and Justine McCulloch for encouraging me and helping in
my experiment and life. Thanks to Amanda Schmidt who taught me how to operate the
Elemental Analyzer. Thanks to Tessa Jongbloets for her great contribution to the field
experiment. Thanks to all volunteers for their help in harvesting.
Special thanks to my parents; I would not be where I am today without their support.

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LIST OF FIGURES
Figure 2.1 1 m2 quadrat frame in place for rough fescue seedling transplants (left), and 9
rough fescue seedlings after transplanting (right). .................................................................. 12
Figure 3.1 Mean total biomass (±1 SE) of Festuca campestris Rydb. and Centaurea Stoebe
L. grown alone at three N/P ratio. Bars sharing the same letter are not significantly different
using Bonferroni (P<0.05) between species. .......................................................................... 32
Figure 3.2 Mean total biomass (±1 SE) of Festuca campestris Rydb. and Centaurea Stoebe
L. grown with conspecific plant at three N/P ratio. Bars sharing the same letter are not
significantly different using Bonferroni (P<0.05) between species. ....................................... 34
Figure 3.3 Competitive importance (±1 SE) of Festuca campestris Rydb. and Centaurea
Stoebe L. grown together. Bars sharing the same letter are not significantly different using
Bonferroni (P<0.05). ............................................................................................................... 36

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LIST OF TABLES
Table 2.1 Mean rough fescue biomass and soil parameters measured within the 40 spotted
knapweed patches and 40 native grass patches with standard error in parentheses. Values in
bold represent significant differences between the two patch size (P<0.05). ......................... 14
Table 2.2 Mean rough fescue biomass and soil parameters measured within the 20 large
spotted knapweed patches and 20 small spotted knapweed patches with standard error in
parentheses. Values in bold represent significant differences between the two patch size
(P<0.05). ................................................................................................................................. 14
Table 3.1 Biochar and sand properties. Analysis done by Ministry of Environment,
Environmental Sustainability and Strategic Policy Division Knowledge Management Branch
– Laboratory using HNO3/HCl Microwave Digest. ................................................................ 28
Table 3.2 Exchangeable Cations and Effective CEC (0.1 M Barium Chloride) of biochar and
sand. Analysis done by Ministry of Environment, Environmental Sustainability and Strategic
Policy Division Knowledge Management Branch – Laboratory. ........................................... 28
Table 3.3 Modified Rorison's nutrient solution as applied to the N: P ratio nutrient treatments
(preparation of 100 mL; Hendry and Grime 1993). α +, the solution was included; , the
solution was omitted from the treatment. ............................................................................... 29
Table 3.4 Results of three-way ANOVA with blocking factor examining the effects of
species, N: P ratio and biochar addition on the mean total biomass of spotted knapweed and
rough fescue (species grown alone). Significant (α<0.05) values in bold. ............................. 31
Table 3.5 Results of two-way ANOVA with blocking factor examining the effects of N: P
ratio and biochar addition on the mean total biomass of spotted knapweed (two same plants
grown together). Significant (α<0.05) values in bold. ............................................................ 33
Table 3.6 Results of two-way ANOVA with blocking factor examining the effects of N: P
ratio and biochar addition on the mean total biomass of rough fescue (two same plants grown
together). Significant (α<0.05) values in bold ........................................................................ 33
Table 3.7 Results of two-way ANOVA with blocking factor examining the effects of N: P
ratio and biochar addition on competitive importance of spotted knapweed (intraspecific
competition). Significant (α<0.05) values in bold. ................................................................. 35
Table 3.8 Results of two-way ANOVA with blocking factor examining the effects of N:P
ratio and biochar addition on competitive importance of rough fescue (intraspecific
competition). Significant (α<0.05) values in bold. ................................................................. 35
Table 3.9 Results of three-way ANOVA with blocking factor examining the effects of
species, N: P ratio, and biochar addition on competitive importance (interspecific
competition). Significant (α<0.05) values in bold. ................................................................. 36

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Chapter 1 ˗ General Introduction
Non-native invasive species are a serious worldwide problem (Reid et al. 2009). Once
established, these exotics can dominate an environment and are hard to control and eliminate.
Invasive plant species can reduce biodiversity, change forage availability for domesticated
and native herbivores and alter soil nutrient properties (Reid et al. 2009). Forests, rangelands,
wetlands and valuable cropland in North America are threatened by non-native invasive
plants, causing substantial economic lose (White & Schwarz 1998).
The success and dominance of invasive plants are suggested to be the result of two
primary factors. First, exotic plant invasives may no longer be in the presence of their natural
enemies from their native distribution; referred to as the enemy-free hypothesis (Andonian &
Hierro 2011). Without their natural enemies, introduced species may quickly grow,
reproduce and expand. The absence of herbivores, pathogens and competitive species in new
habitats can provide an environment with less competition and disturbance for invaders to
grow and multiply at a high rate. Second, the interaction between the soil biota and the
invasive plant species may be mutualistic (Andonian & Hierro 2011). It is possible that
invasive species encounter less inhibitory effects of soil biota where they are introduced than
in their home range. Thus, soil microbes can promote invasion in recipient communities
while inhibiting plants at home.
The management of invasive alien plants is challenging because it often requires
multiple methods at a high cost. Even so, there is evidence of many successful eradication
programs, or at least the maintenance of populations at low densities of exotics (Simberloff
2008). The different methods applied to control invasives include mechanical, physical,
chemical and biological controls.
Grasslands
Grasslands are characterized by the dominance of grasses and forbs rather than large
shrubs and trees, and cover about 3500 million ha of the Earth’s surface (Carlier et al. 2009).
Grasslands contribute to reducing soil erosion and improving soil and water quality (Carlier
et al. 2009). Also, they provide food for livestock and serve as habitat to wildlife thus
enhancing biodiversity (Miller 2013). From an economic perspective, grasslands provide
livelihoods and a major source of income.
Despite the important role of grasslands, they are being threatened by several

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stressors, such as human activities, invasive species and climate change. Grasslands are
converted for agricultural purposes and destroyed due to urban sprawl, thus reducing
biodiversity through loss of habitat (Klaus 2013). Non-native invasive plants species are
detrimental to grasslands through the alteration of disturbance processes, diminishment of the
quality of feed for livestock and wildlife, and the displacement of native plants (Reid et al.
2009). Furthermore, the change of temperature, precipitation, and soil moisture caused by
climate change can influence grassland function, including carbon storage, nitrate filtration,
water quality, and forage for livestock and wildlife (Mannetje 2007).
Spotted knapweed (Centaurea stoebe L.)
Spotted knapweed (Centaurea stoebe L.) is an invasive plant introduced to North
America from Europe. It is a short-lived perennial forb growing from a taproot to erect
stems, ridged and laxly branched (Story et al. 1989). The height of spotted knapweed is 0.21.8 m, with solitary flowering heads at the ends of branches (Province of British Columbia
2002). The spotted appearance is given by stiff and tipped floral bracts with a dark, comblike fringe (Province of British Columbia 2002). The flowers are pinkish purple or, rarely,
cream colored. Its rosette leaves are up to 15 cm long and deeply lobed (Province of British
Columbia 2002). The principal stem leaves are pinnately divided having smooth margins and
getting smaller toward the top of the shoot (Province of British Columbia 2002).
Spotted knapweed is widespread at low- to mid-elevation grasslands and dry open
forests in British Columbia, Canada (Province of British Columbia 2002). It also can be
found on roadsides, fields, and disturbed areas. It is adapted to well-drained, light- to coarsetextured soils but is intolerant to dense shade. The plant is frequent in southern B.C. east of
the Coast-Cascade mountains. It is present on the Mainland and Vancouver Island as well.
Spotted knapweed has become a major concern in the Kootenay, Okanagan, Thompson,
Cariboo, Omineca, and Peace River agricultural reporting regions (Province of British
Columbia 2002).
Spotted knapweed reduces wildlife and livestock forage production, lowers native
biodiversity, and increases loss of soil mineral nutrients (Sheley & Jacobs 1997; Fraser &
Carlyle 2011). Through secreting allelochemicals, shifting microbial mechanism and
affecting resource depletion mechanism, spotted knapweed influences soil properties and
native grasses (Suding et al. 2004). Spotted knapweed contributes to reducing soil nitrogen

3

availability (Hook et al. 2004; Story et al. 1989) and increasing soil phosphorus availability
(Thorpe al. 2006). Hook et al. (2004) reports that spotted knapweed can increase or decrease,
but mostly decrease, soil carbon pools in native grasslands. Spotted knapweed has been
shown to have a greater ability to uptake soil water than native grass, such as Pseudoregneria
spicata and Pascopyron smithii (Hill et al. 2006). In terms of influencing soil properties,
spotted knapweed affects the growth of native plants since the essential nutrients for plant
growth are changed. For example, the growth of rough fescue is restrained by the presence of
spotted knapweed (Fraser and Carlyle 2011). It hinders rough fescue’s growth through
altering soil nutrients, reducing soil nitrogen, carbon and volumetric water content while
increasing soil phosphorus and potassium.
Rough fescue (Festuca campestris Rydb.)
Rough fescue (Festuca campestris Rydb.) is a native, perennial, cool-season
bunchgrass of northwestern North America (USDA-NRCS 2003). The large-diameter
bunches of individual rough fescue plants usually average 30.5 – 35.5 cm in diameter,
sometimes as large as 70.0 cm. The culms are erect, 30.5 to 137.2 cm. tall, glabrous,
scabrous, naked below the panicle, and purplish at the base. Leaves are basal 30.5-76.2 cm
long, 0.08-0.20 cm in diameter, folded, mostly erect, stiff, and pointed. The lower surface of
the leaves are often scabrous (USDA-NRCS 2003).
Rough fescue occurs in grass-dominated and shrub-dominated plant communities. It
also can occur in ponderosa pine woodlands, open ponderosa pine forests, subalpine forests,
and in grassy areas within forests. For example, it occurs in southeastern British Columbia.
Rough fescue grows slowly, which requires 3 to 5 years to become established and produces
seed only every 2 to 10 years (Desserud & Naeth 2013). It prefers fertile mostly black soils
(black chernozem) with ample moisture that is more than 33 cm annual precipitation,
whereas it has been found growing in a 25 cm to 28 cm rainfall area in western Montana
(Baldridge & Lohmiller 1990).
Rough fescue is an ecologically and economically important native plant species
within grasslands of western Canada (Bogen et al. 2002). Rough fescue grassland is an
important habitat for a variety of small mammals and provides forage for wildlife. From an
agricultural and economic perspective, rough fescue grassland provides high quality forage
for livestock (Desserud & Naeth 2013; Desserud et al. 2013). However, rough fescue

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grasslands are considered one of the most threatened grassland communities in western
Canada due to residential development, livestock heavy grazing and non-native species
invasion (Desserud et al. 2013; McInenly et al. 2010). Non-native plant species are
particularly problematic when they are competitively superior to native plants.
Competition and soil nutrients
Competition occurs when resources are in short supply because they have been
consumed by neighboring organisms (Keddy 2001). For plants, intra- or interspecific
competition will arise when they are sharing resources with neighbors. Plants have the same
basic requirements for light, water, and nutrients, and they inevitably shade their neighbors
and/or have somewhat overlapping root systems (McGraw & Chapin 1989). Resource
competition theory shows that a plant population in a monoculture with a single limiting
resource would grow and reduce the concentration of that resource to an equilibria level
where growth would be balanced by losses (Dybzinski & Tilman 2007). When species
compete for a single resource, the species with the lower equilibria level is predicted to win,
as demonstrated for rapidly growing organisms (Dybzinski & Tilman 2007). Rapid nutrient
uptake and effective pre-emption of soil nutrients are critical for plant growth under
competition. Competition among individuals and species of plants may be affected by
nutrient availability and acquisition. The ratio of nitrogen to phosphorus (N:P) availabilities
influence the productivity and species composition of plant communities (Ahmad-Ramli et
al. 2013). Previous studies have shown that different outcomes of species competition under
nitrogen- or phosphorus-limited conditions probably reflects the fact that some species
compete most successfully for nitrogen, while others compete more successfully for
phosphorus (Venterink and Güsewell 2010). A study from Leskovšek et al. (2012)
demonstrates that higher nitrogen availability increases the competitive advantage of invasive
grass (Ambrosia artemisiifolia L.) compared with native grass (Lolium multiflorum L.).
Ahmad-Ramli et al. (2013) show that the availability of phosphorus is increasingly
recognized as a key nutrient that limits productivity, either on its own or in combination with
other mineral nutrients like nitrogen. These previous studies indicate that variations in
nitrogen and phosphorus supply can influence the intensity of competitive interactions and
could potentially affect the outcome of plant competition.

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Biochar
Biochar is the use of charcoal as a soil amendment, which has been proposed to
increase both soil organic carbon levels and soil fertility (Gathorne-Hardy et al. 2009).
Biochar is able to improve soil productivity, carbon storage, or filtration of percolating soil
water (Lehmann & Joseph 2009) because of its two key properties: a high affinity to
nutrients and water, and a long residence time. The high affinity to nutrients and reduces
onsite nutrient loss and offsite pollution from nutrient leaching. The long residence time
leads to biochar’s promotion for carbon sequestration (Gathorne-Hardy et al. 2009).
Biochar’s effects on soil properties may have direct impacts upon plant growth because of
the penetration depth and availability of air and water within the root zone is determined
largely by the physical components of soil (Lehmann & Joseph 2009).
Thesis Research Objectives
The overall objective of this thesis is to study methods to restore spotted knapweed
infested grasslands in British Columbia. The first objective is to understand spotted
knapweed invasion. My thesis examined the carry over effects of recently removed spotted
knapweed on soil properties and vegetation at Lac du Bios Grasslands Provincial Park in
chapter 2. The second objective is to test the ability of biochar to restore grasslands infested
by spotted knapweed in British Columbia. As previous studies have shown positive results on
plant growth with the use of biochar, I conducted a greenhouse experiment to examine
competitive effects of spotted knapweed on rough fescue at different N:P ratios, and with a
biochar addition treatment in chapter 3. The information gained through this study will help
to move the spotted knapweed infested grassland restoration in British Columbia forward.

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References
Ahmad-Ramli, M. F., Cornulier, T., & Johnson, D. (2013). Partitioning of soil phosphorus
regulates competition between Vaccinium vitis-idaea and Deschampsia cespitosa.
Ecology and Evolution, 3(12), 4243–4252.
Alberta, S., Desserud, P. A., & Naeth, M. A. (2013). Smooth Brome: An Unexpected
Response to Straw-Amended Soil (Alberta), 28(2), 133–135.
Andonian, K., & Hierro, J. L. (2011). Species interactions contribute to the success of a
global plant invader. Biological Invasions, 13(12), 2957–2965.
Baldridge, D. E., & Lohmiller, R. G. (1990). Montana Interagency Plant Materials
Handbook for Forage Production, Conservation, Reclamation, and Wildlife. Bozeman,
Montana: Montana State University, Extension Service.
Bogen, A. D., Bork, E. W., & Willms, W. D. (2002). Rough fescue (Festuca campestris
Rydb.) response to heat injury, Canadian Journal of Plant Science, 82, 721-729.
Carlier, L., Rotar, I., Vlahova, M., & Vidican, R. (2009). Importance and Functions of
Grasslands, Notulae Botanicae Horti Agrobotanici Cluj-Napoca, 37(1), 25–30.
Desserud, P., & Naeth, M. A. (2013). Establishment of a native bunch grass and an invasive
perennial on disturbed land using straw-amended soil. Journal of Environmental
Management, 114, 540–547.
Dybzinski, R., & Tilman, D. (2007). Resource use patterns predict long-term outcomes of
plant competition for nutrients and light. The American Naturalist, 170(3), 305–318.
Fraser, L. H., & Carlyle, C. N. (2011). Is spotted knapweed (Centaurea stoebe L.) patch size
related to the effect on soil and vegetation properties?. Plant Ecology, 212, 975-983.
Gathorne-Hardy, A., Knight, J., & Woods, J. (2009). Biochar as a soil amendment positively
interacts with nitrogen fertiliser to improve barley yields in the UK. IOP Conference
Series: Earth and Environmental Science, 6(37), 372052.
Hill, J. P., Germino, M. J., Wraith, J. M., Olson, B. E., Megan, B., Journal, I., Swan, M. B.
(2006). Advantages in Water Relations Contribute to Greater Photosynthesis in
Centaurea maculosa Compared with Established Grasses. International Journal of
Plant Sciences, 167(2), 269–277.
Hook, P. B., Olson, B. E., & Wraith, J. M. (2004). Effects of the invasive forb Centaurea
maculosa on grassland carbon and nitrogen pools in Montana, USA. Ecosystems, 7(6),
686–694.
Keddy, P. A. (2001). Competition (2nd ed.). Boston: KLUWER ACADEMIC
PUBLISHERS.

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Klaus, V. H. (2013). Urban Grassland Restoration: A Neglected Opportunity for Biodiversity
Conservation. Restoration Ecology, 21(6), 665–669.
Lehmann, J., & Joseph, S. (2009). Biochar for Environmental Management: Science and
Technology. UK: Earthscan.
Leskovšek, R., Eler, K., Batič, F., & Simončič, A. (2012). The influence of nitrogen, water
and competition on the vegetative and reproductive growth of common ragweed
(Ambrosia artemisiifolia L.). Plant Ecology, 213(5), 769–781.
Mannetje, L. (2007). Climate change and grasslands through the ages: an overview. Grass
and Forage Science, 62(2), 113–117.
McGraw, J. B., & Chapin, F. S. (1989). Competitive Ability and Adaptation to Fertile and
Infertile Soils in Two Eriophorum Species, Ecology, 70(3), 736–749.
McInenly, L. E., Merrill, E. H., Cahill, J. F., & Juma, N. G. (2010). Festuca campestris alters
root morphology and growth in response to simulated grazing and nitrogen form.
Functional Ecology, 24(2), 283–292.
Miller, C. F. (2013). The evolving understanding of grassland restoration seeding protocols,
Ecological Restoration, 31(2), 127–129.
Province of British Columbia. (2002). Spotted Knapweed (Centaurea biebersteinii DC.). A
Guide to Weeds in British Columbia, 158–161. Open Learning Agency
Reid, A. M., Morin, L., Downey, P. O., French, K., & Virtue, J. G. (2009). Does invasive
plant management aid the restoration of natural ecosystems? Biological Conservation,
142, 2342-2349.
Sheley, R. L., & Jacobs, J. S. (1997). Response of spotted knapweed and grass to picloram
and fertilizer combinations. Journal of Range Management, 50, (3), 263-267.
Simberloff, D. (2008). We can eliminate invasions or live with them. Successful management
projects. Biological Invasions, 11(1), 149–157.
Story, J. M., Boggs, K. W., & Graham, D. R. (1989). Effects of nitrogen fertilization on
spotted knapweed and competing vegetation in western Montana. Journal of Range
Management, 42(3), 222-225.
Suding, K. N., LeJeune, K. D., & Seastedt, T. R. (2004). Competitive impacts and responses
of an invasive weed: Dependencies on nitrogen and phosphorus availability.
Oecologia, 141 (3), 526-535.
Thorpe, A. S., Archer, V., & DeLuca, T. H. (2006). The invasive forb, Centaurea maculosa,
increases phosphorus availability in Montana grasslands. Applied Soil Ecology, 32(1),
118–122.

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United States Department of Agriculture Natural Resources Conservation Service (2003).
Plant Guide.
Venterink, H. O., & Güsewell, S. (2010). Competitive interactions between two meadow
grasses under nitrogen and phosphorus limitation. Functional Ecology, 24(4), 877–886.
White, P. S., & Schwarz, A. E. (1998). Where do we go from here? The challenges of risk
assessment for invasive plants. Weed Technology, 12 (4), 744-751.

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Chapter 2 ˗ Soil Residual Effects of Spotted Knapweed on Soil Properties and
Vegetation at Lac Du Bios Grasslands Provincial Park
Introduction
Soil plays an important role by supporting the growth of plants, controlling the
storage and flow of water in the hydrologic system, facilitating decomposition and nutrient
cycling, providing habitat for living organisms, influencing the composition and physical
condition of the atmosphere and being an engineering medium in human-built ecosystems
(Brady &Weil 2008). Taking this significance into consideration, preserving soil properties is
essential. Available soil nutrients are needed for plant growth; however, non-native invasive
plants can alter soil nutrient availability (Reid et al. 2009).
Soil nitrogen is vital for plant growth and development. Nitrogen is an integral
component of many essential plant compounds, such as amino acids and nucleic acids.
Nitrogen is needed for protein development, photosynthesis and the processing of
carbohydrates within plants (Bang 2007). Nitrogen stimulates root growth and development,
as well as the uptake of other nutrients (Brady &Weil 2008). Soil phosphorus is also
important for plant growth. It plays an important role in photosynthesis, nitrogen fixation,
flowering, fruiting and maturation (Blackshaw & Brandt 2009). Phosphorus encourages root
growth, especially development of lateral roots and fibrous rootlets (Brady &Weil 2008).
Carbon is an essential element of soil organic matter; organic-matter-rich soils are generally
better for plant growth. Organic matter improves soil physical and chemical properties,
which provides suitable plant growing conditions (Smith & Stitt 2007). Volumetric water
content is a key hydrological soil physical variable that influences the hydrological response
of catchment (Dlamini & Chaplot 2012). It influences the partition between runoff and soil
infiltration. It also controls energy and gas fluxes between the pedosphere, the biosphere and
the atmosphere, which greatly influence land processes such as soil water denitrification
(Grimaldi & Chaplot 2000), carbon sequestration, associated climate change and biodiversity
(Asbjornsen et al. 2011). Thus, volumetric water content plays an important role in soil
compaction and provides available water for plant growth.
Spotted knapweed has been shown to reduce soil nitrogen availability and increase
soil phosphorus availability (Story et al. 1989; Hook et al. 2004; Thorpe et al. 2006; Fraser
and Carlyle 2011). Hook et al. (2004) reported that spotted knapweed can increase or

10

decrease, but mostly decrease, soil carbon pools in native grasslands. Fraser and Carlyle
(2011) also reported a decrease in soil carbon in spotted knapweed patches compared to
rough fescue grassland. Spotted knapweed has been shown to have a greater ability to uptake
soil water than native grass (Hill et al. 2006). Spotted knapweed can influence soil properties
but what is not known is whether there are residual effects of spotted knapweed on soil
properties and plant growth after the spotted knapweed has been removed, and whether
potential residual effects might affect the successful re-establishment of native species for
restoration.
Spotted knapweed is a strong competitor with rough fescue and causes reduced
biomass of native grasses (Press et al. 1998; Suding et al. 2004). Spotted knapweed has a
larger leaf area and a higher rate of growth than rough fescue (Press et al. 1998). In addition,
spotted knapweed secretes allelochemicals that negatively affect the growth of native plants
(Suding et al. 2004). The question remains whether it is possible to restore rough fescue
following invasion by spotted knapweed? Press et al. (1998) demonstrated that revegetation
with fast-growing, tall-statured species can be a method of managing spotted knapweed
invasion. Therefore, areas invaded by spotted knapweed may have the potential to be
restored through the removal of spotted knapweed and transplanting rough fescue seedlings.
Fraser and Carlyle (2011) found that large patch size (>10 m2) of spotted knapweed
has been shown to have a greater negative effect on soil properties. Therefore, I hypothesize
that if there are residual soil effects caused by spotted knapweed, these effects will likely be
greater in sites where the knapweed patch size was larger. In my study, residual effects from
spotted knapweed were compared between former large and small patches, and the biomass
accumulation of planted rough fescue seedlings were compared between the different patch
sizes.
The field site study was designed to test the following hypotheses:
(1) Soil nitrogen, carbon, volumetric water content and dry biomass accumulation of
transplanted rough fescue seedlings will be lower in former spotted knapweed patches than in
former native grass patches, but soil phosphorus will be higher.
(2) Soil nitrogen, phosphorus, carbon, volumetric water content and dry biomass
accumulation of transplanted rough fescue seedlings will be lower in former large spotted
knapweed than in former small spotted knapweed patches.

11

(3) Soil nitrogen, carbon and volumetric water content will have a negative linear
relationship on biomass of transplanted rough fescue seedlings within former spotted
knapweed patches, while soil phosphorus will be higher.
Materials and Methods
Site description
The research was done at Lac du Bios Grassland Provincial Park located to the
northwest of the city of Kamloops, British Columbia, Canada (N50°47, W120°26). Soils of
Lac Du Bois Park are classified as Chernozems (van Ryswyk et al. 1966) in accordance with
the Canadian Soil Classification System (Soil Classification Working Group 1998). Within
this park, the dominant grass species are Festuca campestris Rydb., Achnatherum
occidentale (Thurb.) Barkworth ssp. occidentale, and S. richardsonia (Link) Barkworth
described by van Ryswyk et al. (1996). Spotted knapweed first established in this grassland
approximately 40 years ago (Fraser & Carlyle 2011).
The average annual precipitation is about 260 mm, but it increases up to 310 mm
with greater precipitation partly from snow melting at higher elevation in the park (Carlyle et
al. 2011). The highest rainfall is between June and August. The driest period occurs between
March and April. Snow falls mainly in December and January (Ministry of Environment,
Lands and Parks Report 2000). The average temperature in the valley bottom is 8.4 ̊C, and
decreases by approximately 0.5 degrees with an elevation increase every 500 m (Ministry of
Environment, Lands and Parks Report 2000). The upper elevation grasslands in Lac Du Bois
Park have higher annual precipitation and lower mean temperature compared to lower and
middle grasslands.
Experimental design
The study was designed to test carry over effects from recently removed spotted
knapweed. The experiment was established in May 2011 and ended in September 2011.
Forty patches of spotted knapweed (twenty large and twenty small patches) were randomly
selected within Lac Du Bois Provincial Park. A knapweed patch was identified as a group of
at least 10 stems, with stems no further than 0.5 m from its neighbor. Patches were separated
by at least 20 m. Patch size was classified according to a previous study, where a large patch
had an area larger than 10 m2 and a small patch had an area between 2 m2 and 10 m2 (Fraser

12

& Carlyle 2011). Paired patches of the neighboring native species were located 5 m due
North from the edge of the knapweed patch. Within the knapweed and paired native patches,
a 1 m2 area of spotted knapweed and the paired 1 m2 area of neighboring native species were
respectively cleared by removing the above-ground vegetation in mid-May, 2011. Within
each cleared area, nine seedlings of rough fescue were transplanted in a 3×3 array, spaced 30
cm apart (Figure 2.1). The seedlings were about 4 months old, between 5-10 cm tall, and had
been propagated from seed in the Research Greenhouse at Thompson Rivers University,
Kamloops, BC. Seedlings were randomly selected for transplant. Seedlings were watered to
field capacity at the time of the transplant, but there was no further watering.

Figure 2.1 1 m2 quadrat frame in place for rough fescue seedling transplants (left), and 9
rough fescue seedlings after transplanting (right).
Sampling, Measurements and Analysis
On the day of harvesting (mid-September, 2011) the transplanted rough fescue
seedlings, the top 10 cm3 of soil at each corner of the 1 m2 plot was collected with the use of
a soil corer and the four soil samples were combined, stored in zip-lock bags and transported
to the laboratory where they were air dried. Dry soil samples were sieved with 2 mm mesh to
separate coarse fragments, roots and small rocks.
All the transplanted rough fescue seedlings were clipped at the above-ground level in
the last week of September. Biomass of each rough fescue seedling was stored in a paper bag
and transported to the laboratory and oven dried at 75°C for at least 48h, and weighed.

13

Volumetric water content (%) was measured by using a TDR soil moisture meter
fitted with a 20 cm soil rod (Spectrum Technologies, Inc.) at each corner of the 1 m2 plot.
Dry and sieved soil samples were prepared for analysis for total nitrogen, total
phosphorus and total carbon. Soil nitrogen (ppm) and carbon (ppm) were analyzed with a
CE-440 Rapid Analysis Elemental Analyzer, Exeter Analytical, Inc. Total soil phosphorus
(mg·l-1) was measured using Palintest© test kits. The mineral concentration of mg·l-1 is
equivalent to mg kg-1 (i.e. ppm).
Statistical Analysis
First, paired t- tests were used to compare the biomass of rough fescue seedlings and
soil properties within 40 former spotted knapweed patches and within 40 former native grass
patches. Second, 2-sample t-tests were used to compare the biomass of rough fescue
seedlings and soil properties in former large spotted knapweed patches and in former small
spotted knapweed patches. Third, linear regressions were applied to predict the effect of soil
properties on biomass accumulation of rough fescue seedlings. Statistical analysis of the data
was performed using Minitab®16.2.4. All data followed a normal distribution under a
Kolmogorov-Smirnov test or an Anderson-Darling test (Appendix A).
Results
Results from the paired t-test indicated that biomass of transplanted rough fescue
seedlings was higher in the native grass patches compared to the spotted knapweed patches
(Table 2.1). There was no difference in total phosphorus between spotted knapweed and
native grass patches. Total nitrogen, total carbon and volumetric water content were found to
have lower values in the spotted knapweed patches (Table 2.1).
Based on the 2 sample t-test biomass of rough fescue seedlings and all measured soil
variables were found to be not significantly different between the large and small spotted
knapweed patches (Table 2.2).
There were no significant linear regression results between rough fescue biomass and
soil properties (total nitrogen, total phosphorus, total carbon and volumetric water content);
or within former spotted knapweed patches that were large or small.

14

Table 2.1 Mean rough fescue biomass and soil parameters measured within the 40 spotted
knapweed patches and 40 native grass patches with standard error in parentheses. Values in
bold represent significant differences between the two patch size (P<0.05).
Former spotted

Former native

knapweed patches

grass patches

P value

Rough fescue seedlings
Biomass (g)

0.336 (0.024)

0.384 (0.020)

0.052

Total nitrogen (ppm)

4837 (239)

5838 (312)

0.011

Total phosphorus (ppm)

1269.2 (28.3)

1263.6 (27.5)

0.858

Total carbon (ppm)

5103 (279)

6287 (336)

0.008

Volumetric water content (%)

9.648 ( 0.349)

10.68 (0.370)

0.037

Soil variables

Table 2.2 Mean rough fescue biomass and soil parameters measured within the 20 large
spotted knapweed patches and 20 small spotted knapweed patches with standard error in
parentheses. Values in bold represent significant differences between the two patch size
(P<0.05).
Former Spotted Knapweed Patches

P value

(Large)

(Small)

0.365 (0.031)

0.307 (0.035)

0.224

Total nitrogen (ppm)

5026 (415)

4648 (242)

0.436

Total phosphorus (ppm)

1286 (32)

1252 (48)

0.554

Total carbon (ppm)

5295 (492)

4911 (272)

0.499

Volumetric water content (%)

9.90 (0.63)

9.39 (0.31)

0.473

Rough fescue seedlings
Biomass (g)
Soil variables

15

Discussion
Soil nitrogen, carbon, volumetric water content and biomass of transplanted rough
fescue seedlings were lower in former spotted knapweed patches compared to former native
grass patches, which supports my first hypothesis. The result indicates that effects from
spotted knapweed on these three measured soil properties and transplanted rough fescue
seedlings’ biomass accumulation still exist even though the above-ground parts of the spotted
knapweed plants were cleared. In contrast, there was no difference in total soil phosphorus
between former spotted knapweed patches and native grassland. However, Fraser and Carlyle
(2011) showed that soils where spotted knapweed was present had higher concentrations of
total phosphorus compared to grassland soils within the same Lac du Bois grasslands as
studied here. My result suggests that the effects of soil phosphorus caused by spotted
knapweed are relatively transient. Perhaps the planted rough fescue seedlings were able to
uptake the extra available phosphorus in the soil within the former knapweed patches.
Soil nitrogen
Total soil nitrogen was higher in native grasslands compared to former knapweed
patches. Harvey and Nowierski (1989) also found that nitrogen concentration was 62% lower
on soils from a site infested with spotted knapweed than from a site dominated by grasses.
The differentiation in total nitrogen between the former spotted knapweed patches and
former native grass patches may be caused by the high mobility and multiple loss pathways
of mineral soil nitrogen (Schulze 2000). Spotted knapweed is reported to reduce soil nitrogen
availability (Hook et al. 2004; Story et al. 1989). Under this nutrient-deficient condition,
bacteria, decomposer fungi and soil fauna will not mineralise organic nitrogen and not
release ammonium (Schulze 2000). Organic nitrogen mineralization and ammonium release
contribute to soil total nitrogen, so the decrease of them can cause a lower nitrogen level to
knapweed-infested areas than non-infested areas. The lower nitrogen within former spotted
knapweed patches was probably only temporary. Spotted knapweed decreases the rate of
nitrification, which is driven by bacteria and the root exudate catechin (Thorpe and Callaway
2010). However, Thorpe and Callaway (2010) found that the inhibitory effects of catechin on
nitrification decreased over time since some bacteria degrade catechin (Arunachalam et al.
2003) and catechin oxidizes rapidly in solution and in soils (Inderjit et al. 2008; Pollock et al.
2009).

16

Soil carbon
Soil carbon sequestration is limited by the availability of nitrogen and phosphorus (Goll et al.
2012). De Graaff et al. (2006) suggests that the main driver of soil carbon sequestration is
soil carbon input through plant growth, which is strongly controlled by nutrient availability.
Since spotted knapweed reduces soil nitrogen and increases phosphorus, the lower carbon
within former spotted knapweed patches may be a decrease in sequestration of carbon. Soil
carbon is a mixture of different organic molecules, ranging from very labile to very stable
according to their residence time in the soil. Stable carbon is protected against decomposition
by various mechanism including micro-aggregation, association with clay and silt particles
and formation of recalcitrant compounds (Six et al. 2002). Labile carbon is by contrast
affected by rates of decomposition (Epron et al. 2009). (±)Catechin, exudation secreted by
spotted knapweed may accelerate the decomposition of soil organic matter and stimulate the
dissolution of insoluble minerals by rhizosphere microorganisms (Haichar et al. 2014), which
decreases carbon residence time. As a result, a lower carbon level reflected within infested
areas may because of a decrease in carbon sequestration caused by spotted knapweed.
Soil phosphorus
There was no difference in total soil phosphorus between former spotted knapweed
patches and native grassland. Stevenson and Cole (1999) found that spotted knapweed
contains catechin which is important in the complexation of iron (Fe), aluminium (Al), and
calcium (Ca), including the precipitation of Ca–P compounds. As a result, spotted knapweed
can increase soil available phosphorus in the rhizosphere through chelation of metal
elements. Furthermore, the amount of phosphorus taken up by plants is governed by the
equilibria among the numerous phosphorus compounds in the soil and the differing abilities
of plants to modify their rhizosphere environments. In this experiment, there may be three
possibilities why phosphorus in former spotted knapweed infected area was the same as
native grassland: the transplanted rough fescue seedlings may have taken up the soluble
increased phosphorus; the soluble phosphorus was lost as surface runoff during rainfall
events within the year the knapweed was removed and the soil was sampled; or there was no
difference in phosphorus to begin with since the sites were not measured before the rough
fescue was transplanted. The last point, though, is unlikely considering that Fraser and

17

Carlyle 2011) showed significantly higher soil phosphorus in knapweed patches compared to
native grasslands within the same site two years earlier
Soil volumetric water content
Due to a greater access to soil water sources and a greater ability to extract water
from deeper soils for invaders (Hill et al. 2006), spotted knapweed has a greater amount of
water usage than native grasses. As a result, my experiment showed that soil volumetric
water content was higher where the native grass formerly dominated. Gȍrgens and Wilgen
(2004) pointed out that it may take several years before streamflow recovery approaches preplanting levels after clearing of dense and extensive stands of alien plants, which indicates
that invasive plants deplete soil water resources and the water take time to be replenished.
Similarly, loss of soil water within areas invaded by spotted knapweed may take time to
recover. On the other hand, soil water is influenced by soil structure, the more wellaggregated soil the higher the water holding capacity (Liu et al. 2014). Spotted knapweed is
able to change soil aggregation via changes in soil microbial properties or processes (Lutgen
& Rillig 2004). While soil aggregation changed by spotted knapweed, soil structure in
knapweed-infested areas has lower aggregate stability than that in non-infested area. This
explains that the differences in soil volumetric water content may result from variance of soil
aggregation between knapweed-infested and non-infested areas.
Biomass
Plant productivity is controlled by multiple nutrients and their interactions (Estate &
Park 2013). Previous studies have shown that spotted knapweed reduces soil nitrogen and
increases soil phosphorus (Fraser and Carlyle 2011; Thorpe et al. 2006; Olson & Blicker
2003); thus leading to nitrogen limitation for plant growth. In addition, decreased water
availability within the former spotted knapweed patches likely caused a further limitation to
the growth of rough fescue seedlings. Furthermore, spotted knapweed exudes large amounts
of (±)-catechin from its roots, which is highly allelopathic to North American species
(Newingham & Callaway 2006). Thus, it is possible that residual allelochemicals have
effects on plants growth. As a result, the biomass of rough fescue was lower than in the
former native grass dominated area.

18

Differences between large and small patches
There was no difference in soil nitrogen, phosphorus, carbon, volumetric water
content and biomass of transplanted rough fescue seedlings between former large and small
spotted knapweed patches, which does not support my second hypothesis. Fraser & Carlyle
(2011) showed a trend that soil properties (nitrogen, carbon and volumetric water content)
and plant biomass are negatively associated with patch size, while soil phosphorus is
positively associated with patch size. That was a correlative study considering knapweed
biomass as a covariate; it cannot say with certainty that differences in soil properties and
plant biomass were caused by knapweed patch size. Taking this into consideration, the fact
that carry over effects from patch size seemed to make no difference in soil properties and
transplanted rough fescue seedling biomass may be because spotted knapweed was removed.
Results from my experiment indicate that scale may not be an important consideration in the
carry over effects of spotted knapweed on soil properties and rough fescue biomass following
removal of spotted knapweed.
Linear regression
There was no relationship between soil properties (nitrogen, phosphorus, carbon and
volumetric water content) and the biomass of transplanted rough fescue seedlings within
former spotted knapweed patches, which does not support my third and last hypothesis. The
observed differences in plant growth may be due to the complex interactions between soil
properties caused by spotted knapweed, or allelochemicals (Newingham & Callaway 2006);
or due to initial variances among rough fescue seedlings, small differences in initial size and
growth rates between individuals could make differences in a long-term development
(Mangla et al. 2011). Real effects on biomass of rough fescue seedlings can be hidden if
variance in initial single soil nutrient availability (nitrogen, phosphorus, carbon and
volumetric water content) is small compared to differences caused by spotted knapweed.

19

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23

Chapter 3 ˗ Competitive Effects from Spotted Knapweed on Rough Fescue with or
without Biochar Addition at Different N: P Ratios
Introduction
Competition
Competition is the negative effect from one organism on another by consuming a
resource that is limited in availability or controlling access to that resource (Keddy 2001).
Competition occurs when resources are in short supply because they have been consumed by
neighboring organisms (Keddy 2001). For plants, intra- or interspecific competition will arise
when they are sharing resources with neighbors. Plants have the same basic requirements for
light, water, and nutrients, and they inevitably shade their neighbors and/or have somewhat
overlapping root systems (McGraw & Chapin 1989).
Previous studies have shown that the non-native invasive spotted knapweed
(Centaurea stoebe L. subsp. micranthos (Gugler) Hayek) can reduce biomass of native
grasses, which indicates that competition occurs between spotted knapweed and native
grasses, such as rough fescue (Press et al. 1998). The mechanism of spotted knapweed to
successfully out-compete rough fescue is not clear. It could be that allelopathic root exudates
restrain the growth of rough fescue (Suding et al. 2004); or the morphology of spotted
knapweed (rosette leaves and stout taproot) is more competitive (Press et al. 1998); or
spotted knapweed alters soil properties to the detriment of rough fescue growth rate: spotted
knapweed reduces soil nitrogen, carbon, water and increases soil phosphorus, which
influences growth of rough fescue (Story et al. 1989; Hook et al. 2004; Thorpe et al. 2006;
Hill et al. 2006; Press et al. 1998; Fraser & Carlyle 2011). To understand how spotted
knapweed competes with rough fescue I designed a pairwise interaction experiment in the
greenhouse. In this study, N:P ratio was examined as one of factors influencing the growth of
spotted knapweed and rough fescue. Blicker et al. (2002) reported that competition for
nitrogen between spotted knapweed and native grasses is various, which means that spotted
knapweed’s growth response to nitrogen depends on which species it is growing with.
Results from Suding et al. (2004) showed that reduction of soil phosphorus weakened the
ability of C. diffusa to tolerate neighbor competition proportionately more than the other

24

focal species. Similarly, under low phosphorus conditions, spotted knapweed may lose its
competitive advantage.
N:P ratio
Soil nitrogen and phosphorus are vital for plant growth and development; however,
they are often among the most limiting nutrients, especially in grassland soils (Olson &
Blicker 2003; Goll et al. 2012). While the availability of nitrogen and phosphorus is often
dynamic and changeable, the growth of spotted knapweed can influence soil nutrient
availability. For example, Callaway et al. (2004) has shown that spotted knapweed increases
phosphorus availability; but Hook et al. (2004) and Story et al. (1989) has shown that spotted
knapweed reduces nitrogen availability. Fraser and Carlyle (2011) have also found that
spotted knapweed patches have higher amounts of phosphorus and lower amounts of nitrogen
in soils compared to areas where rough fescue grows.
Plants are usually exposed to multiple resource limitations, which is saying that they
are limited by nitrogen, phosphorus, or other resources (e.g., light, CO2, and water) at the
same time. An increase in nitrogen limitation may create greater limitation in phosphorus
(Baldwin 2013). In addition, individual plants within a diverse community may have
different competitive abilities for various limiting resources. They can experience greater or
lesser limitation to different resources depending on their morphology and physiology. For
example, plants with larger roots may be competitively superior in soil mineral nutrient
resource acquisition compared to plants with smaller roots (Baldwin 2013). On the other
hand, the availability of nitrogen and phosphorus influences plant performance, plant species
interactions and multi trophic interactions (Baeten et al. 2011). Consequently, altering the
levels of nitrogen and phosphorus supply may have a significant impact on the growth of
spotted knapweed and rough fescue and interactions between these two species. This study
was conducted with three N:P ratios (1:1, 15:1 and 30:1) to determine how nutrient supply
affects competition between spotted knapweed and rough fescue.
Biochar
Biochar is a soil amendment that is produced by thermal decomposition of organic
material (forest residues such as bark, sawdust, and shavings; and agricultural wastes such as

25

wheat straw and bagasse) under limited supply of oxygen and at relatively low temperatures
(< 700 °C). Biochar is used to improve soil productivity, carbon storage, or filtration of
percolating soil water (Lehmann & Joseph 2009). The study of biochar is growing due to its
perceived ability to increase plant yields while at the same time reduce the need for fertilizer,
to decrease soil nutrient runoff losses and reduce atmospheric carbon through the
sequestration of carbon in the soil (America et al. 2007). Despite the positive effects
attributed to biochar soil amendment, little research has been published elucidating the
mechanisms and effects of biochar.
Biochar is considered to have positive effects on plants through influencing soil
nutrient availability, such as potentially immobilizing plant-available nitrogen (Ventura et al.
2013). The added biochar is thought to stimulate nitrogen mineralization thereby improving
nitrogen uptake by plants (Saarnio et al. 2013). Gathorne-Hardy et al. (2009) have shown that
biochar appears to increase nitrogen use efficiency of crops when it is applied with N
fertilizer. Similar to the impacts on soil nitrogen, biochar affects availability of phosphorus
for plants (Biederman & Harpole 2013). Studies have shown that biochar can increase soil
phosphorus availability through several mechanisms; for example, Parvage et al. (2012),
Lehmann and Joseph (2009) demonstrate that biochar is a direct source of soluble
phosphorus and can serve as a binder for positively charged metal complexes (Al3+, Fe3+2+,
Ca2+). These studies suggest that biochar has the potential to affect plant growth through
increasing the availability of soil nitrogen and phosphorus for plant uptake. These changes of
soil properties caused by biochar can influence plant growth (Devereux et al. 2013).
However, the impact of biochar on plants is still not comprehensive since it is highly variable
depending on the properties of the biochar and the soil, plant species and environmental
conditions (Saarnio et al. 2013).
The availability of nitrogen and phosphorus influences plant performance, plant
species interactions and multi trophic interactions (Baeten et al. 2011). The growth of spotted
knapweed can influence soil nutrient availability. For example, Hook et al. (2004) and Story
et al. (1989) have shown that spotted knapweed reduces nitrogen availability; but Callaway et
al. (2004) have shown that spotted knapweed increases phosphorus availability. So, by
manipulating nutrient supply through differing N:P ratios I can test whether spotted
knapweed will have a greater growth response under a higher relative phosphorus

26

concentration. Whereas, biochar is more likely to increase nitrogen availability and to bind
phosphorus (Gathorne-Hardy et al. 2009; Parvage et al. 2012; Lehmann and Joseph 2009),
which could reduce the growth potential of spotted knapweed.
The greenhouse study was designed to test three hypotheses:
(1) Biomass of spotted knapweed will be greater at 1:1 N:P ratio, and relatively less
so at 15:1 and 30:1 N:P ratios; whereas rough fescue will show the opposite response.
(2) Biomass of spotted knapweed is less when grown in biochar, compared to grown
in pure sand. In contrast, biomass of rough fescue is greater when grown in biochar,
compared to grown in pure sand.
(3) Competitive importance decreases for spotted knapweed with increasing N:P
ratios and biochar addition, whereas it increases for rough fescue with increasing N:P ratios
and biochar addition.
Materials and Methods
Experimental design
The design was a 5 plant by 3 nutrient supply ratio by 2 biochar factorial combination
replicated 8 times for a total of 240 treatment combinations. The five plant treatments
included spotted knapweed alone, rough fescue alone, two spotted knapweed, two rough
fescue and the two species in a pair wise interaction; the three nutrient supply ratios included
N:P ratios of 1:1, 15:1 and 30:1; and the two biochar additions treatments consisted of a
biochar added or not.
Species
Spotted knapweed is a short-lived perennial forb and an aggressive weed that reduces
wildlife and livestock forage production, lowers native biodiversity, and increases loss of soil
mineral nutrients (Sheley & Jacobs 1997; Fraser & Carlyle 2011) in British Columbia,
Canada. Rough fescue (Festuca campestris Rydb.) is an ecologically and economically
important native plant species within grasslands of western Canada (Bogen et al. 2002).
Greenhouse conditions
The climate, temperature and relative humidity, were electronically controlled during
February and May in 2013. Daytime temperature was maintained at 25°C and night time

27

temperature at 17°C (Hendry & Grime 1993). The relative humidity was held constant at
55% for both daytime and night time. Three 1000W halogen sulphide lamps supplied
supplemental light for 14 hours in the day. Pots were divided into eight blocks and randomly
arranged within each block.
Germination
Approximately 600 seeds of spotted knapweed and rough fescue were placed in
separated plastic Petri dishes filled with a sand medium (fine-textured Home Depot© Play
Sand) saturated with water. The Petri dishes were placed in the greenhouse receiving 16h of
light. Rough fescue seeds were sown 4 days before spotted knapweed seeds to ensure
germination of both species occurred within days of each other.
Treatments
Seedlings were transplanted from Petri dishes into 1.3 L round pots, (11.4 cm high,
15.2 cm diameter, with 8 drain holes). Each pot was filled with 1 L pure sand (Table 3.1&
3.2). Each pot received one or two transplants: spotted knapweed alone, rough fescue alone,
two spotted knapweed together, two rough fescue together, spotted knapweed with rough
fescue.
Each species combination that included a biochar addition were treated with 10 grams
of biochar (Table 3.1 & 3.2). The application rate was biochar to soil ratio of 1:69 on a mass
basis (Ameloot et al.2013). Biochar was mixed with sand medium one week before the sand
was saturated with water. The sand medium was saturated with water immediately prior to
transplantation. Three days after planting, each planting combination was watered with 100
mL modified Rorison’s nutrient solution (Hendry & Grime 1993) (Table 3.3) at three
different ratios of nitrogen to phosphorus (N:P) every three days: 1:1, 15:1 and 30:1 N:P.

28

Table 3.1 Biochar and sand properties. Analysis done by Ministry of Environment,
Environmental Sustainability and Strategic Policy Division Knowledge Management Branch
– Laboratory using HNO3/HCl Microwave Digest.
Element

Biochar

Sand

Element

Biochar

Sand

Ca (%)

2.129

1.042

Mo (ppm)

3.9

1.0

Mg (%)

0.243

0.718

Zn (ppm)

613.4

90.4

K (%)

0.532

0.261

Cu (ppm)

36.4

31.6

Fe (%)

1.641

2.022

Total P (ppm)

1004

446

Al (%)

0.323

1.489

Total N (%)

0.442

0.006

Na (%)

487

855

Total C (%)

79.35

0.13

Mn (ppm)

1106

368

pH

9.80

7.99

B (ppm)

23.1

5.0

Table 3.2 Exchangeable Cations and Effective CEC (0.1 M Barium Chloride) of biochar and
sand. Analysis done by Ministry of Environment, Environmental Sustainability and Strategic
Policy Division Knowledge Management Branch – Laboratory.
Element(cmol+/Kg) Biochar

Sand

Element(cmol+/Kg)

Biochar

Sand

Al

0.303

0.002

Mg

0.523

0.320

Ca

8.073

1.967

Mn

0.007

0.003

Fe

0.005

<0.001

Na

0.229

0.060

K

1.864

0.062

CEC

11.00

2.41

29

Table 3.3 Modified Rorison's nutrient solution as applied to the N: P ratio nutrient treatments
(preparation of 100 mL; Hendry and Grime 1993). α +, the solution was included; , the
solution was omitted from the treatment.
-1

N:P ratioα

Element

mg. 100mL

Stock solutions

Ca/N

8.0/5.60

Mg

1: 1

15: 1

30: 1

Ca(NO3)2·4H2O

+

+

+

2.4

MgSO4·7H2O

+

+

+

K/P

14.2/5.60

K2HPO4·3H2O

+

+



K/P

0.4/0.18

K2HPO4·3H2O





+

Fe

0.3

Fe EDTA

+

+

+

Mn

0.06

MnSO4·4H2O

+

+

+

B

0.06

H3BO3

+

+

+

Mo

0.01

(NH4)6Mo7O24·4H2O

+

+

+

Zn

0.01

ZnSO4·7H2O

+

+

+

Cu

0.01

CuSO4·5H2O

+

+

+

K

6.81

K2SO4 (0.5molL-1)





+

Harvesting
Harvesting occurred on Day 90. Individuals were separated by species and then by
above-ground and below-ground biomass. The biomass samples were dried for 48 hours at
70°C and weighed.
Statistical analysis
To analyze mean potential biomass I used only the data for plants grown alone. A log
transformation was done for these data; they follow a normal distribution under an AndersonDarling test and have equal variances under a Levene’s test (Appendix B). An ANOVA
(Minitab®16.2.4) was conducted to test the effects of species, N:P ratios and biochar
addition on the total plant biomass (α=0.05). A log transformation was done for the data
when plants grown alone and two rough fescues grown together for using ANOVA
(Appendix B). The data used for testing competitive importance with intraspecific

30

competition had a normal distribution under an Anderson-Darling test and had equal
variances under a Levene’s test (Appendix B). A reciprocal transformation was done for the
data when plants grown with interspecific competition. The data had a normal distribution
under an Anderson-Darling test and had equal variances under a Levene’s test (Appendix B).
Competitive importance was calculated using the equation: Cimp =𝑀𝑃

𝑃−𝑁 −𝑃+𝑁
±𝑁 −min⁡(𝑃−𝑁⁡ ,𝑃+𝑁 )

, where

P-N is plant grown without neighbors (alone) and P+N is plant grown with neighbors, and
MP±N is the maximum value of plant performance in the studied system, regardless of
neighbors (Seifan et al. 2010— modified after Brooker et al. 2005). In this equation, the
index has a limited range of -1 to1; where negative values represent competitive interaction
and positive values represent facilitation. The importance of competition is a relative
measure of the effect of competition at a point along the gradient relative to other processes,
it can incorporate the role of other processes in describing the impact of competition (Gilbert
& Fraser, 2013).
Results
Total biomass
Plants grown alone
The mean total dry biomass of plants when grown alone (without competition) was
significantly affected by two of the three main effects (species and N: P ratio) but not by
biochar addition (Table 3.4). Spotted knapweed had a greater mean biomass (4.83g ± 0.45
SE) than rough fescue (0.786 ± 0.094 SE). Biochar did not affect plant biomass.
An interaction between species and N:P ratios was shown to be not significant (Table
3.4). However, results showed that spotted knapweed had the greatest biomass at 1:1 N/P
ratio, whereas rough fescue had the greatest biomass at 15:1 N/P ratio. Spotted knapweed’s
biomass was greater at 15:1 N/P ratio compared to 30:1 N/P ratio. Rough fescue’s biomass
was greater at 1:1 N/P ratio compared to 30:1 N/P ratio. Biomass of spotted knapweed was
greater than that of rough fescue at each N/P ratio (Fig. 3.1).
The two-way interaction between species and biochar addition was not significant,
neither the interaction between N: P ratio and biochar addition was significant (Table 3.4).

31

Table 3.4 Results of three-way ANOVA with blocking factor examining the effects of
species, N: P ratio and biochar addition on the mean total biomass of spotted knapweed and
rough fescue (species grown alone). Significant (α<0.05) values in bold.
Source

Mean squares

Degree of freedom

F ratio

P value

Block

0.115

7

1.71

0. 125

Species

10.823

1

160.97

<0.001

N:P ratio

1.625

2

24.17

<0.001

Biochar

0.067

1

0.99

0.323

Species × N:P ratio

0.131

2

1.94

0.153

Species × Biochar

0.037

1

0.56

0.459

N:P ratio × Biochar

0.071

2

1.05

0.356

Species × N:P ratio × Biochar

0.017

2

0.26

0.775

Error

0.067

56

32

8

Festuca campestris Rydb.
Centaurea Stoebe L.

b

7
b

Total Biomass (g)

6
5
4
3

c

2

a

a

c

1

N:P

0

1:1

15:1

30:1

Figure 3.1 Mean total biomass (±1 SE) of Festuca campestris Rydb. and Centaurea Stoebe
L. grown alone at three N/P ratio. Bars sharing the same letter are not significantly different
using Bonferroni (P<0.05) between species.
Pairwise intraspecific interactions
The mean total dry biomass of plants when grown together (with intraspecific
competition) was significantly affected by N:P ratio but not by biochar addition for both
species (Table 3.5 & Table 3.6); the mean total dry biomass of rough fescue (with
intraspecific competition) had significant block effect (Table 3.6). Spotted knapweed had a
greater mean biomass (5.98g ± 0.54 SE) than rough fescue (1.104 ± 0.081 SE).
Results showed that spotted knapweed had the greatest biomass at 1:1 N/P ratio.
Spotted knapweed’s biomass was greater at 15:1 N/P ratio compared to 30:1 N/P ratio. On
the other hand, N/P ratio did not result in any significant differences to rough fescue’s
biomass. The biomass of spotted knapweed was greater than that of rough fescue at each N/P
ratio (Fig. 3.2).
The two-way interaction between N:P ratio and biochar addition was not significant
for either species (Table 3.5 & Table 3.6).

33

Table 3.5 Results of two-way ANOVA with blocking factor examining the effects of N: P
ratio and biochar addition on the mean total biomass of spotted knapweed (two same plants
grown together). Significant (α<0.05) values in bold.
Source

Mean squares

Degree of freedom

F ratio

P value

Block

3.531

7

0.57

0.776

N:P ratio

145.331

2

23.36

<0.001

Biochar

2.582

1

0.41

0.524

N: P ratio × Biochar

4.557

2

0.73

0.489

Error

6.221

30

Table 3.6 Results of two-way ANOVA with blocking factor examining the effects of N: P
ratio and biochar addition on the mean total biomass of rough fescue (two same plants grown
together). Significant (α<0.05) values in bold
Source

Mean squares

Degree of freedom

F ratio

P value

Block

0.055

7

3.03

0. 013

N:P ratio

0.103

2

5.65

0.007

Biochar

0.001

1

0.03

0.867

N: P ratio × Biochar

0.012

2

0.66

0.524

Error

0.018

35

34

b

9

Festuca campestris Rydb.
Centaurea Stoebe L.

8

b

Total Biomass (g)

7
6
5
4
3
2

a
a

a

1
0

a

1:1

15:1

30:1

Figure 3.2 Mean total biomass (±1 SE) of Festuca campestris Rydb. and Centaurea Stoebe
L. grown with conspecific plant at three N/P ratio. Bars sharing the same letter are not
significantly different using Bonferroni (P<0.05) between species.
Competitive importance
For both species, competitive importance was not significant by any main effects
(N:P ratio and biochar addition) when plants grown with intraspecific competition, neither
was it significantly affected by a two-way interaction between N:P ratio and biochar addition
(Table 3.7 & Table 3.8).

35

Table 3.7 Results of two-way ANOVA with blocking factor examining the effects of N: P
ratio and biochar addition on competitive importance of spotted knapweed (intraspecific
competition). Significant (α<0.05) values in bold.
Source

Mean squares Degree of freedom

F ratio P value

Block

0.059

7

0.60

0.751

N:P ratio

0.145

2

1.51

0.235

Biochar

0.179

1

1.86

0.182

N:P ratio × Biochar

0.264

2

2.75

0.078

Error

0.096

35

Table 3.8 Results of two-way ANOVA with blocking factor examining the effects of N:P
ratio and biochar addition on competitive importance of rough fescue (intraspecific
competition). Significant (α<0.05) values in bold.
Source

Mean squares

Degree of freedom

F ratio

P value

Block

0.1946

7

1.32

0. 268

N:P ratio

0.0317

2

0.22

0.807

Biochar

0.0919

1

0.63

0.434

N: P ratio × Biochar

0.1735

2

1.18

0.319

Error

0.1469

35

Competitive importance was significantly affected by one of the three main effects
(species), but not by N: P ratio or biochar addition when plants grown with interspecific
competition (Table 3.9). Results showed that there was a competitive interaction with spotted
knapweed, the value of competitive importance was -0.136 ± 0.052 SE; whereas rough
fescue demonstrated a facilitation response, the value of competitive importance was 0.0200
± 0.0068 SE (Fig. 3.3). This shows that spotted knapweed had a stronger competitive ability
than rough fescue when grown together.
The two-way interaction between species and N: P ratio was not significant, neither
the interaction between species and biochar addition was significant, nor the interaction
between N: P ratio and biochar addition was significant.

36

Table 3.9 Results of three-way ANOVA with blocking factor examining the effects of
species, N: P ratio, and biochar addition on competitive importance (interspecific
competition). Significant (α<0.05) values in bold.
Source

Mean squares

Degree of freedom

F ratio

P value

Block

0.07796

7

1.18

0. 323

Species

0.58144

1

8.82

0.004

N:P ratio

0.08055

2

1.22

0.300

Biochar

0.09861

1

1.50

0.225

Species × N: P ratio

0.12673

2

1.92

0.153

Species × Biochar

0.07089

1

1.08

0.303

N: P ratio × Biochar

0.02261

2

0.34

0.711

Species × N: P ratio × Biochar

0.00770

2

0.12

0.890

Error

0.06594

77

a

Competitive importance

0.00

-0.05

-0.10

-0.15
Festuca campestris Rydb.
Centaurea Stoebe L.

-0.20

b

Figure 3.3 Competitive importance (±1 SE) of Festuca campestris Rydb. and Centaurea
Stoebe L. grown together. Bars sharing the same letter are not significantly different using
Bonferroni (P<0.05).

37

Discussion
Total biomass
The results partially supported my first hypothesis because total biomass of spotted
knapweed when grown alone was greatest at 1:1 N/P ratio and declined as N/P ratio
increased. Total biomass for both species when two of the same plants grown together was
greater at 1:1 N: P ratio, and relatively less so at 15:1 and 30:1 N: P ratios. Because a good
supply of nitrogen stimulates root growth and development, and spotted knapweed prefers a
high level of nitrogen (Blicker et al. 2002); spotted knapweed had its greatest biomass at 1:1
N/P ratio when grown alone and grown with its conspecific plant. Due to the polymorphism
of spotted knapweed, intraspecific competition may not be strong enough to be shown under
these N:P ratios. Güsewell (2005) suggests that all species seems to have maximum biomass
at an N: P supply ratio of 15:1 within a level of light and nutrient supply. The result that
rough fescue had greatest biomass at 15:1 N: P ratio when grown alone accords with
Güsewell (2005). However, the results when two rough fescues grown together are different
from when it is grown alone because the condition for growth has been changed. In the
presence of a competitor, competition for nutrients generates a condition where plants must
allocate more resources to acquisition of the limiting resource than is optimal for plants in the
absence of competition (Craine 2006). Due to this condition, biomass of rough fescue may be
influenced. As a consequence, the biomass of rough fescues grown together is different from
when grown alone.
Differing from my prediction, biochar addition made no significant differences in
total biomass of both species when plants grown alone or grown together. Desserud and
Naeth (2013) suggest that smooth brome (Bromus inermis), another non-native introduced
from Europe and Eurasia in the late 1880s, has a strong negative reaction to straw-amended
soils. For native grasses, biochar addition increases biomass of plants regardless of variability
introduced by soil and climate (Biederman & Harpole 2013). On the contrary, biomass of
spotted knapweed and rough fescue were not significantly affected by biochar addition in my
experiment. Nitrogen is volatilized in proportion to carbon and associated with the carbon in
the retained fraction sharing its recalcitrance. Therefore, the fact that biochar addition did not
work as expected might be that nitrogen is not always the limiting resource for plant growth.

38

Competitive importance
Neither N:P ratio, biochar addition nor the interaction between N:P ratio and biochar
addition significantly influenced competitive importance for intraspecific interactions..
Previous research has indicated that increased nitrogen favors invasive and decreased
nitrogen availability favors native species (Mangla et al. 2011). Considering this, spotted
knapweed should have a stronger competition with increasing N:P ratio and rough fescue
should have a stronger competition with decreasing N:P ratio. Intraspecific competition had
no different response to biochar for spotted knapweed and rough fescue. Previous study
indicated that spotted knapweed is able to avoid intraspecific competition since they display
germination and emergence polymorphism (Interference et al. 2013). Intraspecific
competition is strongly dependent upon the growth environment (Keddy 2001), for that
reason, intraspecific competition of rough fescue might not show in this experiment.
However, small differences in initial size and growth rates between individuals could
potentially make differences in long-term development (Mangla et al. 2011). Since spotted
knapweeds and rough fescues were transplanted into pots at early stage and they were
affected by N: P ratio and biochar, there might be differences in competition between
individuals for a longer period of experiment.
Competitive interactions drove spotted knapweed responses while facilitation drove
the response of rough fescue when the two species were grown together regardless of N:P
ratio and biochar addition, which means that spotted knapweed was a stronger competitor.
Suding et al. (2004) reported that Centaurea diffusa remained the best competitor under low
nitrogen conditions, while lost its competitive advantage under low phosphorus conditions.
Therefore, Centaurea stoebe L. should have significant responses to various N:P ratios.
Ridenour and Callaway (2001) showed that activated charcoal (which adsorbs organic
compounds, similar to biochar) reduced the apparent allelopathic effect of Centaurea stoebe
L. on Festuca idahoensis in sand culture. It suggests that the balance of competition in favor
of Centaurea had been shifted by activated carbon. Biochar addition should have similar
effects on rough fescue grown with spotted knapweed. However, the results from my study
has shown that biochar addition had no effect, perhaps because the contact time between soil
and biochar was not long enough or biochar was not activated before its application.

39

The availability of nitrogen and phosphorus influences plant performance, plant
species interactions and multi trophic interactions (Baeten et al. 2011). In general, the
growth of spotted knapweed and rough fescue had significant responses to N:P ratio but not
to biochar addition. Various N:P ratios and biochar addition did not reduce competition of
spotted knapweed on rough fescue.

40

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Hill, J. P., Germino, M. J., Wraith, J. M., Olson, B. E., Megan, B., Journal, I., Swan, M. B.
(2006). Advantages in Water Relations Contribute to Greater Photosynthesis in
Centaurea maculosa Compared with Established Grasses. International Journal of Plant
Sciences, 167(2), 269–277.
Hook, P. B., Olson, B. E., & Wraith, J. M. (2004). Effects of the invasive forb Centaurea
maculosa on grassland carbon and nitrogen pools in Montana, USA. Ecosystems, 7(6),
686–694.
Interference, S. K., Sheley, R. L., & Jacobs, J. S. (2013). Influence of density on intermediate
wheatgrass and spotted knapweed interference, 50(5), 523–529.
Keddy, P. A. (2001). Competition (2nd ed.). Boston: KLUWER ACADEMIC
PUBLISHERS.
Lehmann, J., & Joseph, S. (2009). Biochar for Environmental Management: Science and
Technology. UK: Earthscan.
Mangla, S., Sheley, R. L., James, J. J., & Radosevich, S. R. (2011). Intra and interspecific
competition among invasive and native species during early stages of plant growth.
Plant Ecology, 212(4), 531–542.
McGraw, J. B., & Chapin, F. S. (1989). Competitive Ability and Adaptation to Fertile and
Infertile Soils in Two Eriophorum Species, Ecology, 70(3), 736–749.
Olson, B. E., & Blicker, P. S. (2003). Response of the invasive Centaurea maculosa and two
native grasses to N-pulses, Plant and Soil, 254, 457–467.
Parvage, M. M., Ulén, B., Eriksson, J., Strock, J., & Kirchmann, H. (2012). Phosphorus
availability in soils amended with wheat residue char. Biology and Fertility of Soils,
49(2), 245–250.

42

Press, A., Sheley, R. L., Jacobs, J. S., & Carpinelli, M. F. (1998). Distribution, Biology, and
Management of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed
(Centaurea maculosa), Weed Technology, 12 (2), 353-362.
Ridenour, W. M., & Callaway, R. M. (2001). The relative importance of allelopathy in
interference: the effects of an invasive weed on a native bunchgrass. Oecologia, 126(3),
444–450.
Saarnio, S., Heimonen, K., & Kettunen, R. (2013). Biochar addition indirectly affects N2O
emissions via soil moisture and plant N uptake. Soil Biology and Biochemistry, 58, 99–
106.
Sheley, R. L., & Jacobs, J. S. (1997). Response of spotted knapweed and grass to picloram
and fertilizer combinations. Journal of Range Management, 50, (3), 263-267.
Story, J. M., Boggs, K. W., & Graham, D. R. (1989). Effects of nitrogen fertilization on
spotted knapweed and competing vegetation in western Montana. Journal of Range
Management, 42(3), 222-225.
Suding, K. N., LeJeune, K. D., & Seastedt, T. R. (2004). Competitive impacts and responses
of an invasive weed: Dependencies on nitrogen and phosphorus availability.
Oecologia, 141 (3), 526-535.
Thorpe, A. S., Archer, V., & DeLuca, T. H. (2006). The invasive forb, Centaurea maculosa,
increases phosphorus availability in Montana grasslands. Applied Soil Ecology, 32(1),
118–122.
Ventura, F., Salvatorelli, F., Piana, S., Pieri, L., & Pisa, P. R. (2013). The effects of biochar
on the physical properties of bare soil. Earth and Environmental Science Transactions
of the Royal Society of Edinburgh, 103, 1–7.

43

Chapter 4 – General conclusions, management implications and directions for future
research
Conclusion
Lac du Bios grasslands are within the temperate grasslands of the southern interior
British Columbia, which are a small but unique ecosystems. Unfortunately, they are being
threatened by several factors, including the invasion of spotted knapweed. Invasive plants
cause loss of biodiversity.
Carry over effects from spotted knapweed on soil properties and plant growth are
important considerations when managing invasion. Previous studies have shown that spotted
knapweed decreases some soil properties (nitrogen, carbon and water), but increases soil
phosphorus (Hook et al. 2004; Story et al. 1989; Thorpe al. 2006; Hill et al. 2006). In
addition, previous study has shown that the level of soil properties and biomass of plants are
lower in large spotted knapweed patches than in small ones (Fraser and Carlyle 2011). While
this evidence partially helps understand spotted knapweed invasion, my study on residual soil
effects from spotted knapweed extends the understanding in spotted knapweed invasion.
This study has shown that soil properties (nitrogen, carbon and volumetric water
content) and biomass of rough fescue are in a lower level because of spotted knapweed, even
though spotted knapweed had been removed for three months. In contrast, soil phosphorus in
former spotted knapweed patches was the same concentration as native grassland. Besides,
there was no differences in soil properties (nitrogen, carbon, phosphorus and volumetric
water content) and biomass of rough fescue between large spotted knapweed patches and
small ones. This information on residual effects from spotted knapweed gives a general idea
on how to restore areas infected by spotted knapweed.
Ridenour and Callaway (2001) showed that activated charcoal (which adsorbs organic
compounds, similar to biochar) reduced the apparent allelopathic effect of Centaurea stoebe
L. on Festuca idahoensis in sand culture. It suggests biochar can be considered as a potential
material to restrain the ability of spotted knapweed to compete with native grasses. However,
biochar used in my experiment seems to have no effect on competitive ability of spotted
knapweed. N: P ratios were also manipulated to determine the effect on spotted knapweed.
This study showed that biomass of plants is influenced by N: P ratio, but competitive

44

importance is not. This information provides evidence that spotted knapweed growth may be
restrained by increasing N: P ratio.
In conclusion, this short-term study identifies immediate impacts on specific
processes that occur in soils and plants, but only long-term data provide confirmation that
these effects are having a significant influence on soils and plants over time. Even so, this
study extends the understanding of spotted knapweed invasion and offers a potential method
to mitigate spotted knapweed invasion.
Management implications
Lac Du Bois grasslands are traditionally used for cattle grazing. To maintain
biodiversity in this community, it is important understand the controlling factors. Invasion of
spotted knapweed is one of those factors. This study has provided information on how to
manage spotted knapweed.
Soil nitrogen, phosphorus, carbon and volumetric water content are essential elements
of soil. The carry over effects from spotted knapweed on those soil properties were tested to
provide directions for managing invasion. To restore infected areas, the solution can be
improving soil properties which are altered by spotted knapweed. Biomass of plants grown in
former infected areas are lower. Plant growth is poor in a soil environment with limited
nutrients. Altering N: P ratios can be seen as a means of improving soil properties. Since N:
P ratio plays a significant role in plant growth, manipulating N: P ratio in this study is a step
to figure out the most unsuitable condition for spotted knapweed growth. To sum up, the key
to recover spotted knapweed invasion is to improve soil properties.
Besides, there is no significant findings by comparing soil properties and biomass of
plants between former large spotted knapweed patches and former small spotted knapweed
patches. Even so, it is a worthy factor to be considered when managing spotted knapweed. It
is common that a smaller problem is easier to solve.
Future research directions
In this study, residual soil effects from spotted knapweed were independently tested.
Instead, current effects and carry over effect should be processed within the same study. To
be specific, soil sampling should be done twice: once immediately after spotted knapweed is
cleared; the second time after transplanted rough fescue seedlings are harvested. Through
comparing these two data points, a more persuasive result could be obtained to better

45

represent carry over effects from spotted knapweed. In addition, a long term study could
provide evidence for residual effects from spotted knapweed.
This study has shown that N: P ratio affects spotted knapweed. It is possible to
manage spotted knapweed invasion through improving infested soil properties. For example,
a suitable N: P ratio for native grasses could enhance their competitive ability when they
compete with spotted knapweed, helping to restrain spotted knapweed invasion.
Biochar is considered as a potential material to restore spotted knapweed. In this
study, 10 g were used to each pot without making any difference in the results. In future
study, different amounts should be tried to see if biochar really has no effects on spotted
knapweed. Biochar made from different materials may have various influences on plant
growth (Ameloot et al. 2013). If conditions allow, various biochars should tested. Last but
not the least, biochar is more effective when mixed with soil for a long time. A biochar study
needs to be longer to ensure the impact is properly tested.

46

References
Ameloot, N., De Neve, S., Jegajeevagan, K., Yildiz, G., Buchan, D., Funkuin, Y. N., Sleutel,
S. (2013). Short-term CO2 and N2O emissions and microbial properties of biochar
amended sandy loam soils. Soil Biology and Biochemistry, 57, 401–410.
Fraser, L. H., & Carlyle, C. N. (2011). Is spotted knapweed (Centaurea stoebe L.) patch size
related to the effect on soil and vegetation properties?. Plant Ecology, 212, 975-983.
Hill, J. P., Germino, M. J., Wraith, J. M., Olson, B. E., Megan, B., Journal, I., Swan, M. B.
(2006). Advantages in Water Relations Contribute to Greater Photosynthesis in
Centaurea maculosa Compared with Established Grasses. International Journal of Plant
Sciences, 167(2), 269–277.
Hook, P. B., Olson, B. E., & Wraith, J. M. (2004). Effects of the invasive forb Centaurea
maculosa on grassland carbon and nitrogen pools in Montana, USA. Ecosystems, 7(6),
686–694.
Ridenour, W. M., & Callaway, R. M. (2001). The relative importance of allelopathy in
interference: the effects of an invasive weed on a native bunchgrass. Oecologia, 126(3),
444–450.
Story, J. M., Boggs, K. W., & Graham, D. R. (1989). Effects of nitrogen fertilization on
spotted knapweed and competing vegetation in western Montana. Journal of Range
Management, 42(3), 222-225.
Thorpe, A. S., Archer, V., & DeLuca, T. H. (2006). The invasive forb, Centaurea maculosa,
increases phosphorus availability in Montana grasslands. Applied Soil Ecology, 32(1),
118–122.

47

Appendix A
99

Mean
StDev
N
KS
P-Value

95
90

-0.04773
0.1508
40
0.098
>0.150

80

Percent

70
60
50
40
30
20
10
5

1

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Differences in rough fescue biomass between spotted knapweed and native grass patches

Figure A. 1 Normality of rough fescue seedlings’ biomass in former spotted knapweed
patches and native grass patches under a Kolmogorov-Smirnov test (P<0.05).

48

99

95
90

Mean
StDev
N
AD
P-Value

-1001
2364
40
0.676
0.072

80

Percent

70
60
50
40
30
20
10
5

1

-7500
-5000
-2500
0
2500
5000
Differences in nitrogen between spotted knapweed and rough fescue patches

Figure A. 2 Normality of total nitrogen in former spotted knapweed patches and native grass
patches under an Anderson-Darling test (P<0.05).

49

99

95
90

Mean
StDev
N
KS
P-Value

5.538
193.8
40
0.085
>0.150

80

Percent

70
60
50
40
30
20
10
5

1

-500
-250
0
250
500
Differences in phosphorus between spotted knapweed and native grass patches

Figure A. 3 Normality of total phosphorus in former spotted knapweed patches and native
grass patches under a Kolmogorov-Smirnov test (P<0.05).

50

99

95
90

Mean
StDev
N
KS
P-Value

-1185
2675
40
0.131
0.082

80

Percent

70
60
50
40
30
20
10
5

1

-8000 -6000 -4000 -2000
0
2000
4000
6000
8000
Differences in carbon between spotted knapweed and native grass patches

Figure A.4 Normality of total carbon in former spotted knapweed patches and native grass
patches under a Kolmogorov-Smirnov test (P<0.05).

51

99

Mean
StDev
N
KS
P-Value

95
90

-1.027
3.014
40
0.129
0.093

80

Percent

70
60
50
40
30
20
10
5

1

-10

-5

0

5

10

Differences in volumetric water content between spotted knapweed and native grass patches

Figure A. 5 Normality of volumetric water content in former spotted knapweed patches and
native grass patches under a Kolmogorov-Smirnov test (P<0.05).

52

99

Mean
StDev
N
KS
P-Value

95
90

0.05830
0.1857
20
0.140
>0.150

80

Percent

70
60
50
40
30
20
10
5

1

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

Differences in rough fescue biomass between former large and small spotted knapweed patches

Figure A. 6 Normality of rough fescue’s biomass in former large and small spotted knapweed
patches under a Kolmogorov-Smirnov test (P<0.05).

53

99

95
90

Mean
StDev
N
KS
P-Value

-0.02842
0.9238
20
0.081
>0.150

80

Percent

70
60
50
40
30
20
10
5

1

-2
-1
0
1
2
Differences in nitrogen between former large and small spotted knapweed patches

Figure A. 7 Normality of total nitrogen in former large and small spotted knapweed patches
under a Kolmogorov-Smirnov test (P<0.05).

54

99

95
90

Mean
StDev
N
KS
P-Value

34.16
245.9
20
0.191
0.054

80

Percent

70
60
50
40
30
20
10
5

1

-500
-250
0
250
500
750
Differences in phosphorus between former large and small spotted knapweed patches

Figure A. 8 Normality of total phosphorus in former large and small spotted knapweed
patches under a Kolmogorov-Smirnov test (P<0.05).

55

99

95
90

Mean
StDev
N
KS
P-Value

383.9
2177
20
0.190
0.057

80

Percent

70
60
50
40
30
20
10
5

1

-5000
-2500
0
2500
5000
Differences in carbon between former large and small spotted knapweed patches

Figure A. 9 Normality of total carbon in former large and small spotted knapweed patches
under a Kolmogorov-Smirnov test (P<0.05).

56

99

Mean
StDev
N
KS
P-Value

95
90

0.5012
2.830
20
0.193
0.050

80

Percent

70
60
50
40
30
20
10
5

1

-5.0

-2.5

0.0

2.5

5.0

7.5

Differences in volumetric water content between former large and small spotted knapweed patches

Figure A. 10 Normality of volumetric water content in former large and small spotted
knapweed patches under a Kolmogorov-Smirnov test (P<0.05).

57

99

95
90

Mean
StDev
N
KS
P-Value

4837
1511
40
0.130
0.086

80

Percent

70
60
50
40
30
20
10
5

1

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Total Nitrogen within Former 40 Spotted Knapweed Patches

Figure A. 11 Normality of total nitrogen in former 40 spotted knapweed patches under a
Kolmogorov-Smirnov test (P<0.05).

58

99

Mean
StDev
N
KS
P-Value

95
90

1269
179.1
40
0.099
>0.150

80

Percent

70
60
50
40
30
20
10
5

1

800 900 1000 1100 1200 1300 1400 1500 1600 1700
Total Phosphorus within 40 Former Spotted Knapweed Patches

Figure A. 12 Normality of total phosphorus in former 40 spotted knapweed patches under a
Kolmogorov-Smirnov test (P<0.05).

59

99

Mean
StDev
N
KS
P-Value

95
90

5103
1765
40
0.128
0.096

80

Percent

70
60
50
40
30
20
10
5

1

0

2000
4000
6000
8000
10000
Total Carbon within 40 Spotted Knapweed Patches

12000

Figure A. 13 Normality of total carbon in former 40 spotted knapweed patches under a
Kolmogorov-Smirnov test (P<0.05).

60

99

95
90

Mean
StDev
N
KS
P-Value

9.648
2.206
40
0.119
>0.150

80

Percent

70
60
50
40
30
20
10
5

1

5.0
7.5
10.0
12.5
15.0
17.5
Volumetric Water Content within 40 Former Spotted Knapweed Patches

Figure A. 14 Normality of volumetric water content in former 40 spotted knapweed patches
under a Kolmogorov-Smirnov test (P<0.05).

61

Appendix B

Normal Probability Plot
(response is total biomass)

99.9

N
AD
P-Value

99

75
0.610
0.109

95

Percent

90
80
70
60
50
40
30
20
10
5
1
0.1

-0.8

-0.6

-0.4

-0.2

0.0
0.2
Residual

0.4

0.6

0.8

Figure B. 1 Normality of potential biomass using 3-way ANOVA when plants grown alone
under an Anderson-Darling test (P<0.05).

62

Test for Equal Variances for Total Biomass
Species

N:P

RF

1:1

Biochar Addition
No
Yes

15:1

No
Yes

30:1

No

Bartlett's Test
Test Statistic
P-Value

20.66
0.037

Levene's Test
Test Statistic
P-Value

1.38
0.204

Yes
SK

1:1

No
Yes

15:1

No
Yes

30:1

No
Yes

0.0
0.5
1.0
1.5
2.0
95% Bonferroni Confidence Intervals for StDevs

Figure B. 2 Equal Variances of potential biomass using 3-way ANOVA when plants grown
alone under a Levene’s test (P<0.05).

63

Normal Probability Plot
(response is Total biomass)

99

N
AD
P-Value

95

43
0.397
0.355

90

Percent

80
70
60
50
40
30
20
10
5

1

-5.0

-2.5

0.0
2.5
Residual

5.0

7.5

Figure B. 3 Normality of potential biomass using 3-way ANOVA when two spotted
knapweeds grown together under an Anderson-Darling test (P<0.05).

64

Test for Equal Variances for Total biomass
N:P

Biochar Addition

1:1

No
Yes

Bartlett's Test
Test Statistic
P-Value

Levene's Test
Test Statistic
P-Value

15:1

10.07
0.073
1.55
0.199

No
Yes

30:1

No
Yes
0
2
4
6
8
10
12
95% Bonferroni Confidence Intervals for StDevs

Figure B. 4 Equal Variances of potential biomass using 3-way ANOVA when two spotted
knapweeds grown together under a Levene’s test (P<0.05).

65

Normal Probability Plot
(response is Total Biomass)

99

N
AD
P-Value

95

36
0.378
0.390

90

Percent

80
70
60
50
40
30
20
10
5

1

-2

-1

0
Residual

1

2

Figure B. 5 Normality of potential biomass using 3-way ANOVA when two rough fescues
grown together under an Anderson-Darling test (P<0.05).

66

Test for Equal Variances for Total Biomass
N:P

Biochar Addition

1:1

No
Yes

Bartlett's Test
Test Statistic
P-Value

Levene's Test
Test Statistic
P-Value

15:1

17.50
0.004
2.52
0.051

No
Yes

30:1

No
Yes
0
1
2
3
4
5
95% Bonferroni Confidence Intervals for StDevs

Figure B. 6 Equal Variances of potential biomass using 3-way ANOVA when two rough
fescues grown together under a Levene’s test (P<0.05).

67

Normal Probability Plot

(response is Competitive Importance)
99

N
AD
P-Value

95

48
0.531
0.167

90

Percent

80
70
60
50
40
30
20
10
5

1

-1.00

-0.75

-0.50

-0.25
0.00
Residual

0.25

0.50

Figure B. 7 Normality of competitive importance using 3-way ANOVA when two spotted
knapweeds grown together under an Anderson-Darling test (P<0.05).

68

Test for Equal Variances for Competitive Importance
N:P_1

Biochar Addition_1

1:1

No
Yes

Bartlett's Test
Test Statistic
P-Value

Levene's Test
Test Statistic
P-Value

15:1

14.64
0.012
1.61
0.177

No
Yes

30:1

No
Yes
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
95% Bonferroni Confidence Intervals for StDevs

Figure B. 8. Equal Variances of competitive importance using 3-way ANOVA when two
spotted knapweeds grown together under a Levene’s test (P<0.05).

69

Normal Probability Plot

(response is Competitive Importance)
99

N
AD
P-Value

95

44
0.573
0.129

90

Percent

80
70
60
50
40
30
20
10
5

1

-1.0

-0.5

0.0
Residual

0.5

1.0

Figure B. 9 Normality of competitive importance using 3-way ANOVA when two rough
fescues grown together under an Anderson-Darling test (P<0.05).

70

Test for Equal Variances for Competitive Importance
N:P

Biochar Addition

1:1

No
Yes

Bartlett's Test
Test Statistic
P-Value

Levene's Test
Test Statistic
P-Value

15:1

13.48
0.019
1.51
0.209

No
Yes

30:1

No
Yes
0.0
0.5
1.0
1.5
2.0
2.5
95% Bonferroni Confidence Intervals for StDevs

Figure B. 10 Equal Variances of competitive importance using 3-way ANOVA when two
rough fescues grown together under a Levene’s test (P<0.05).

71

Normal Probability Plot

(response is Competitive Importance)
99.9

N
AD
P-Value

99

86
0.498
0.206

95

Percent

90
80
70
60
50
40
30
20
10
5
1
0.1

-4

-3

-2

-1

0
Residual

1

2

3

Figure B. 11 Normality of competitive importance using 3-way ANOVA when spotted
knapweed and rough fescue grown together under an Anderson-Darling test (P<0.05).

72

Test for Equal Variances for Competitive Importance
Species

N:P

RF

1:1

Biochar Addition
No
Yes

15:1

No
Yes

30:1

No

Bartlett's Test
Test Statistic
P-Value

23.07
0.017

Levene's Test
Test Statistic
P-Value

1.35
0.216

Yes
SK

1:1

No
Yes

15:1

No
Yes

30:1

No
Yes

0
1
2
3
4
5
6
7
95% Bonferroni Confidence Intervals for StDevs

Figure B. 12 Equal Variances of competitive importance using 3-way ANOVA when spotted
knapweed and rough fescue grown together under a Levene’s test (P<0.05).