12-year N addition enhances soil organic carbon decomposition by mediating microbial community composition in temperate plantations

Soil respiration is a crucial contributor to atmospheric CO2 flux and microbial communities play a vital role in carbon cycling in terrestrial ecosystems. However, the response of microbial community characteristics (such as diversity and composition) and their roles in regulating soil respiration under nitrogen (N) deposition remain unclear. Here, we conducted a 12-year N addition experiment (0, 2, 5, 10 g N m−2 year−1) in a temperate plantation to elucidate the mechanisms of autotrophic respiration and heterotrophic respiration in response to environmental and microbial factors. The results showed heterotrophic respiration increased significantly only under high-N addition (10 g N m−2 year−1), and autotrophic respiration decreased significantly under moderate-N (5 g N m−2 year−1) and high-N addition (10 g N m−2 year−1). The decrease in autotrophic respiration was primarily driven by environmental factors, such as soil pH and N availability, whereas the increase in heterotrophic respiration resulted from changes in the microbial community. Fungi Leotiomycetes, Sordariomycetes, and Rhizophydiomycetes were identified as the key microbial predictors influencing heterotrophic respiration under N addition. Our work identified the role of soil microbial community composition in promoting soil organic matter decomposition under long-term N deposition. And we emphasized the importance of incorporating microbial community information into ecosystem models to improve predictions of climate‑carbon cycle feedbacks. •Long-term nitrogen addition significantly decreased soil autotrophic respiration but increased heterotrophic respiration.•Soil microbial communities, especially fungal communities, regulated the promotion of soil organic matter decomposition under nitrogen addition.•Key microbial predictors of heterotrophic respiration under nitrogen addition were fungi Leotiomycetes, Sordariomycetes, and Rhizophydiomycetes.