Recent multi-factor experiments suggest that interactions among environmental changes commonly influence biodiversity and community composition. However, most field experiments focus on single factors, ignoring interacting stressors. Soil food webs are critical to ecosystem health and may be particularly sensitive to interactions among environmental changes that include soil warming, eutrophication, and altered precipitation regimes. Here we asked, how do environmental changes interact to alter nematode diversity, abundance, community composition, and functional groups in a northern Chihuahuan Desert grassland? We used factorial manipulations of nitrogen, winter rainfall, and nighttime warming to match predicted environmental change scenarios for the region. Warming reduced nematode diversity by 25% and genus-level richness by 32%, but these declines dissipated with additional winter rain, suggesting the warming effect may occur via drying. Under ambient precipitation, nitrogen fertilizer reduced bacterivores by 68% and herbivores by 73% but had no significant influence on fungivores. In contrast, when combined with winter rain addition, nitrogen fertilization instead increased bacterivores by 95%, had no effect on herbivores, and doubled the number of fungivores. Interactive effects of precipitation and nitrogen altered community composition of genus-level nematode abundances, but total nematode abundance was less sensitive than composition or diversity, indicating that most change involved the reordering of species abundances. Nematode community metrics were not tightly coupled to plant community composition in this semi-arid grassland, and may instead track microbes, including biocrusts and decomposers. Our results highlight the importance of interactions among environmental change stressors for the composition and function of soil food webs in drylands.
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