Soil Microorganisms Mediated the Responses of the Plant-Soil Systems of Neotrinia splendens to Nitrogen Addition and Warming in a Desert Ecosystem

Covering about 30% of the global total land area, desert ecosystems have been influenced by warming and nitrogen deposition. However, it remains unclear how desert ecosystems respond to warming and nitrogen deposition. Therefore, we conducted a greenhouse experiment to examine the impacts of N addition and warming on the plant-soil system of Neotrinia splendens, the dominant plant in the desert ecosystem in Northern China. Our findings revealed that low-N dose (N-1) and high-N dose additions (N-2) increased the biomass by 22.83% and 54.23%, respectively; meanwhile, moderate warming (T-2) and severe warming (T-3) decreased the biomass by 39.07% and 45.47%, respectively. N addition did not significantly affect the C:N:P stoichiometry in the plant-soil system. T-2 and T-3 decreased the leaf N content by 17.50% and 16.20%, respectively, and decreased the leaf P content by 10.61% and 45.29%, respectively. This resulted in the plant C:N ratio, C:P ratio, and N:P ratio increasing with warming. Furthermore, warming or N addition not only decreased soil microbial diversity, but also inhibited microbial genera associated with nutrient cycling, such as that of Tumebacillus spp., Bacillus spp., and Mortierella spp.; it additionally influenced important bacterial functions, such as nitrate reduction and ureolysis. Moreover, warming and N addition induced P limitation in the plant-soil system by inhibiting soil microorganisms, such as Mortierella spp. and Bacillus spp., which are associated with P transformation; this was also brought about by increasing the effects of leaf P content on leaf N:P. In conclusion, our results showed that warming and N addition had significant effects on the C:N:P stoichiometry of the plant-soil system through microbial mediation and led to P limitation in the system, regardless of how they affected biomass. Soil microorganisms could mediate the impacts of environmental changes on the plant-soil system. Our findings may provide valuable insights for adjusting vegetation restoration strategies in desert ecosystems under environmental changes.