Effects of simulated N deposition on soil microbial communities among three hydraulically contrasting years in a semi-arid grassland, China

Background/Question/Methods Low critical load of N for grassland soil indicated its sensitivity to N deposition. With ever-increasing nitrogen (N) deposition, soil will become less limited by N availability. Annual variation of soil moisture caused by different precipitation pattern fundamentally impacts on the terrestrial ecosystem, especially semi-arid ecosystems. The joint effect of N and soil moisture on semi-arid grasslands has been reported to be significant yet inconsistent, resulting in a poor understanding of how soil microbial communities respond to N deposition and the variation of soil moisture among years.

Results/Conclusions In this study, N addition was found to be the primary factor in regulating both microbial biomass and composition, while soil moisture indirectly modified soil microbial composition by regulating soil nutrient availability. N addition shifted soil community to bacteria-dominated, but low soil moisture shifted soil community to fungi-dominated. Soil dissolved organic carbon (DOC), soil pH, C: N ratio, ammonium nitrogen and total nitrogen were significantly associated with the variation of microbial composition. Therefore, this study revealed the responses of microbial communities to both factors of N deposition and hydraulically contrasting years, and explored the associations among environmental variables and microbial communities in the semi-arid grassland of China.