Drought and defoliation affect soil extracellular enzyme activity in northern temperate grasslands

Drought has the most significant impact on arid grassland ecosystems. Managed grazing, including the timing and intensity of defoliation, may interact with drought to differentially affect processes related to soil organic matter decomposition. Extracellular enzyme activity (EEA) provides integrated measure of soil microbial activity which affects nutrient cycling. This study examined EEAs in response to five defoliation regimes and drought at seven grasslands across temperate grasslands of Canada. All sites were dominated by perennial grasses and forbs, but differed in plant species, climate, and soils. Soil samples were analyzed for five EEAs involved in carbon (C), nitrogen (N) and phosphorus (P) cycling. Drought reduced activity of enzymes involved in C cycling, β-glucosidase and β-cellobiosidase by 16 and 17%, respectively, P cycling (acid phosphatase) by 11%, and N cycling (N-acetyl-β-glucosaminidase) by 12%. β-xylosidase showed close association with, and was not affected by drought, suggesting a reduction in C turnover under future drought. β-glucosidase activity was reduced by intermediate defoliation relative to both control and heavy. Acid phosphatase and N-acetyl-β-glucosaminidase were affected by three-way interaction of drought, defoliation and mean growing season precipitation, highlighting the complex mechanism underlying EEA responses. Findings suggest that EEA was affected by drought, but defoliation effects were largely dependent upon drought and local climate.