Contrasting effects of warming and N deposition on soil microbial functional genes in a subtropical forest

Abstract Climate warming and nitrogen (N) deposition are expected to increase in the coming decades. The consequences of the interaction between warming and N deposition on forest ecosystems and their functions (i.e., carbon sequestration) remain uncertain. In this study, we examined the composition, diversities, and abundances of soil microbial functional genes in a subtropical forest after four years of exposure to warming and N addition. We found that warming alone did not have a significant effect on the composition, diversities, and abundances of functional genes, suggesting that four years were not long enough to reach the critical threshold that would activate a response to warming from soil functional genes in the subtropical forest. Conversely, warming significantly decreased soil labile carbon (C) content. The application of N in combination with warming significantly enhanced the diversities and abundances of functional genes associated with C and N cycling, leading to an accelerated loss of soil N. Interestingly, the interaction between warming and N addition did not have a significant effect on the diversities and abundances of functional genes associated with C and N cycling. Redundancy analysis indicated that a decrease in pH caused by N addition significantly affected the abundances of those functional genes. Overall, our study fills a research gap by examining the effect of simultaneous warming and N deposition on soil microbial functional genes in subtropical forests. Additionally, the study indicates that microbial functional genes are more sensitive to a combination of warming and N addition than to warming alone. Therefore, the effects of multi-factor global change on soil microbial functional genes cannot be underestimated.