LB 24-210 - Temporal intensity of grazing alters predator-prey relationships in the soil microbiome

Grasslands are reservoirs of soil biodiversity worldwide, covering about one-third of terrestrial ecosystems. While livestock grazing is a common management practice, it can also alter soil microbial communities with subsequent implications for soil nutrient cycling and ecosystem services. Our knowledge regarding the impact of grazing on soil microbiomes remains limited. In particular, we do now know how grazing intensity may affect soil protists that are considered the drivers of soil microbial communities. Here we assessed soil bacterial, fungal, and protist communities under four levels of temporal grazing intensity: no grazing (0 days), low grazing (27 days), moderate grazing (54 days), and heavy grazing (74 days). We hypothesized that (i) soil microbial community will differ across grazing intensities, and (ii) grazing intensity will promote predator-prey interactions. We found grazing caused significant changes in the soil nitrogen and carbon pools. While there were no major changes in bacterial and fungal diversity, heavy grazing intensity significantly increased the diversity of protists. Grazing intensity also significantly altered the community structure of all three microbial groups. Predator protists strongly associated with the prey groups, indicating their nature of being bacterivores or fungivores. Heavy grazing intensity facilitated putative predator-prey relationships with a strong effect on protist:bacteria+fungi ratio (R2=0.72; P=0.0024). Overall, this study highlights how grazing intensity impacts soil microbial dynamics.