Simulated nitrogen deposition decreases soil microbial diversity in a semiarid grassland, with little mediation of this effect by mowing

Atmospheric nitrogen (N) deposition has important effects on soil microbial community diversity and composition. While it is well-known that mowing, a widely used grassland management strategy, could mediate the impacts of N enrichment on macro-organism community composition, much less known is the infra-annual variation of soil microbial community and their responses to N deposition and mowing. Here, we examined the responses of soil bacteria and fungi communities to N deposition and mowing in four months of different seasons in a semiarid grassland in northern China. Nitrogen addition significantly reduced alpha-diversity and changed the community composition of both bacteria and fungi communities across generally all months, possibly due to N-induced soil acidification. Mowing did not affect soil microbial community diversity and did not mediate the impacts of N addition. Soil microbial community diversity and composition significantly varied across different months. Such temporal variation of soil microbial community composition was much greater than the variation resulting from N addition and mowing. Our results suggest that the negative impacts of N enrichment on soil bacteria and fungi diversity are temporally consistent and are unaffected by plant biomass removal.