Winter Foraging by Migratory Ungulates Modifies the Composition and Function of Soil Microbial Communities

Abstract

Saprotrophic microbial communities in soil are commonly thought to be structured by bottom-up ecological forces that arise from resource availability (i.e., plant detritus). However, it is plausible that ungulate foraging could indirectly modify resource availability by altering plant community composition, thereby exerting an indirect, top-down ecological force on soil microbial communities. To test this idea, we quantified microbial community taxonomic composition and functional potential inside and outside of four long-term winter foraging exclosures in sagebrush steppe in Wyoming, USA. Winter foraging exclusion significantly increased Artemisia tridentata biomass and reduced forb percent cover (-6 %). The change in plant composition caused significant changes in microbial taxonomic composition and functional potential by altering the composition of bacteria and fungi with lignocellulolytic function. Our observations provide evidence that winter foraging by ungulates in the sagebrush steppe exerts an indirect top-down ecological force that shapes the composition and function of soil microbial communities.