Nitrogen deficiency in soil mediates multifunctionality responses to global climatic drivers

Natural and anthropogenic processes that decrease the availability of nitrogen (N) frequently occur in soil. Losses of N may limit the multiple functions linked to carbon, N and phosphorous cycling of soil (soil multifunctionality, SMF). Microbial communities and SMF are intimately linked. However, the relationship between soil microbial communities and SMF in response to global changes under N deficiency has never been examined in natural ecosystems. Here, soil samples from nine temperate arid grassland sites were used to assess the importance of microbial communities as driver of SMF to climate change and N deficiency. SMF was significantly decreased by drought and drought-wetting cycles, independent of the availability of soil N. Interestingly, temperature changes (variable temperature and warming) significantly increased SMF in N-poor conditions. However, this was at the expense of decreased SMF resistance. Deterministic assembly-driven microbial α-diversity and particularly fungal α-diversity, but not β-diversity, were generally found to play key roles in maintaining SMF in N-poor soil, irrespective of the climate. The results have two important implications. First, the absence of the stability offered by β-diversity means N-poor ecosystems will be particularly sensitive to global climate changes. Second, fungi are more important than bacteria for maintaining SMF in N-poor soil under climate changes.