Warming enhances the effects of nitrogen addition on fungal but not on bacterial diversity in an alpine meadow

Abstract

Warming and nitrogen (N) deposition significantly affect soil microbial community characteristics. However, the responses of bacterial and fungal diversity to warming and N deposition, as well as the dominant influencing factors, remain unclear, especially in N-limited and low-temperature ecosystems. We employed a field-controlled experimental design with warming (W, using open-top chambers at +2 °C), N addition (N, 40 kg N ha⁻¹ yr⁻¹ NH₄NO₃), and their interaction (NW) to simulate their effects on soil microbial community composition and diversity, as well as plant community characteristics. Our results showed a significant decrease in bacterial richness (Chao1) under warming. N addition had a positive effect on bacterial richness (Chao1) but a negative effect on fungal diversity (Shannon and Chao1), which led to a considerable shift in bacterial community composition. Conversely, N addition combined with warming significantly increased fungal diversity but decreased bacterial diversity compared with N addition alone. Bacterial diversity was positively influenced by soil moisture but negatively affected by soil temperature and forb dominance. Fungal diversity was negatively influenced by soil NH₄⁺-N content and belowground biomass. Additionally, our results showed a synergistic effect on fungi owing to changes in plant community composition, while an antagonistic effect on bacterial diversity was observed owing to reduced water and nutrient availability under warming plus N addition. Our findings underscore the importance of considering plant productivity and diversity when examining microbial diversity responses to warming and N addition in alpine meadows.