Tracking soil temperature and moisture in a multi-factor climate experiment in temperate grassland: Do climate manipulation methods produce their intended effects?

Passive open-top chambers (OTCs) and rainout shelters (RSs) have been used for over two decades to manipulate temperature and water availability in experiments on plant communities. These types of manipulations have been independently evaluated; however, as experiments become more complex and multiple factors are evaluated the potential for unknown or undesirable treatment effects increases. We present the effects of temperature manipulations (with OTCs), water manipulations (with RSs and water additions), and a clipping treatment, implemented in a fully factorial design, on soil moisture and temperature over 2 years in a temperate grassland. Temperature was increased 0.2C by OTCs. Soil volumetric water content was reduced 3% by RSs and increased 2% by watering. However, clipping vegetation, treatment interactions, and weather conditions also affected soil temperature and moisture. For example, in OTCs RSs increased the temperature an additional 0.4C, watering lowered it 0.4C, and clipping raised temperature 2C. Similarly, changes in soil moisture due to the RSs decreased VWC by 3% and increased 1% by clipping whereas soil moisture due to watering was reduced 1% by the OTCs and clipping. We also found that OTCs are more effective at raising temperatures on cooler days when soil temperatures are below 16.3C. Our results suggest that all treatment types generally affect soil variables in predicable ways, but use of such devices should be adopted with caution, as they do not act independently, or exclusively, on the target variables. Key