Defoliation intensity and elevated precipitation effects on microbiome and interactome depend on site type in northern mixed-grass prairie

Soil microorganisms play critical roles in maintaining ecological functions of the northern mixed-grass prairie. While defoliation regimes and elevated precipitation affect plant community composition and primary productivity in these grasslands, their effects on soil microbiome and interactome have not been studied. We examined the response of soil microbiome and interactome to long-term (2010-2015) treatments of varying defoliation regimes (low vs. high intensity and low vs. high frequency) and two precipitation conditions (ambient vs. elevated) on two contrasting sites (a dry vs. a mesic site) in a northern mixed-grass prairie. High intensity defoliation reduced alpha-diversity and altered the beta-diversity of soil microbial communities in the mesic site but not in the dry site, while elevated precipitation reduced alpha-diversity and altered the beta-diversity of soil microbial communities in both sites. Defoliation and precipitation did not show interaction effects on overall alpha- and beta-diversity, but did combine to influence the interactome network. High intensity defoliation promoted the oligotrophic genera Spartobacteria (Verrucomicrobia), Pseudonocardia (Actinobacteria), and Conexibacter (Actinobacteria), while elevated precipitation promoted the copiotrophic genera Nitrososphaera (Thaumarchaeota), Anderseniella (Proteobacteria), Sphingomonas (Proteobacteria), and Acidobacteria Gp16 (Acidobacteria). High intensity defoliation increased the number of linkages for Alphaproteobacteria and Acidobacteria, and decreased the number of linkages for Gemmatimonadetes and Spartobacteria in the interactome networks. However, elevated precipitation increased the number of linkages for Actinobacteria and Gemmatimonadetes and decreased the number of linkages for Spartobacteria and Acidobacteria. Our results show that defoliation intensity and elevated precipitation affected the microbiome and associated interactome network within soils of the northern mixed-grass prairie by affecting different functional taxonomic groups, indicating distinct scenarios for defoliation and precipitation in affecting soil microbial communities.