The interactive effects of manipulated drought and grazing on extracellular enzyme activity in grassland soils across Alberta, Canada

Grassland ecosystems cover approximately 25% of the world's terrestrial land, store about 10% of global soil carbon and are a potential sink for additional carbon. Proper grazing management has been suggested as a way to increase soil carbon, but the effects of grazing may vary across climate conditions and vegetation types. Furthermore, drought may alter the carbon balance in these systems. Here, we examined the effects of grazing and drought on extracellular enzymes (β-glucosidase, acid phosphatase, β-cellobiosidase, N-acetyl-β-glucosaminidase and β-xylosidase) related to carbon, nitrogen and phosphorus release in the soil. Extracellular enzymes may provide an early indication of the response of these systems to changes in grazing management and climate. In 2016, an experiment was established to study the effect of different simulated grazing treatments and drought (ambient vs 45% reduction in precipitation) on extracellular enzyme activity (EEA) at seven grassland sites located across a climate gradient in Southern Alberta. Five simulated grazing treatments were applied, namely light, heavy, light-heavy, heavy-heavy and control based on the intensity and frequency of plant defoliation. Soil samples were collected at 0-15cm depth in 2017. Preliminary results showed that the activity of β-glucosidase, acid phosphatase and β-cellobiosidase was significantly higher in ambient than in drought conditions at one of the wetter sites. While at one of the dryer sites, the activity of β-glucosidase and β-cellobiosidase was significantly higher in ambient than in drought conditions. Furthermore, results showed that the EEA was correlated with soil moisture content and pH. However, no effect of simulated grazing treatments on EEA was detected for the first year.