Get reliable science

Grasslands cover > 40 % of the Earth's surface and contain ca. 30 % of soil organic carbon (SOC) globally. Due to their large size and reserves of SOC, there has been recent interest in improving estimates of SOC pools and their dynamics under management. Previous work shows that grazing and climate have the potential to alter plant communities, which may affect SOC cycling in soils. To better understand how community changes affect SOC, we studied the effect of grazing and moisture availability on the microbial extracellular enzymatic activity (EEA) that ultimately controls SOC cycling. We sampled soils to 10 cm depth within a long-term simulated grazing and grassland watering study taking place in Mixedgrass Prairie vegetation at the Rangeland Research Institute's Mattheis Ranch near Brooks, Alberta, Canada. Our two study sites sit on contrasting ecosites (upland loamy sand soil and a low-lying sandy loam soil). At each site there are replicate plots where simulated summer-long grazing (i.e., clipping) at different frequency (high, low and control) and intensity (high, low) have been applied in conjunction with watering treatments (elevated and ambient). After three years of treatments we observed clear divergence in plant community composition and structure under these treatments (i.e., increaser and decreaser grasses). To assess the effect of defoliation, moisture and associated plant community shifts on carbon stores, we measured SOC, nitrogen, soil organic matter content, soil moisture and EEA in our samples. We hypothesize that SOC cycling via EEA will be greater in plots where moisture is high and defoliation is high (frequency and intensity) due to a biological response tied to the rapid turnover of defoliation tolerant increaser grasses. We will present our findings in the context of simulated grazing intensity and frequency, moisture treatments and changes in community production and diversity.