Soil Enzyme Activities and Microbial Carbon Pump Promote Carbon Storage by Influencing Bacterial Communities Under Nitrogen-Rich Conditions in Tea Plantation

Carbon–nitrogen (C-N) coupling is a fundamental concept in ecosystem ecology. Long-term excessive fertilization in tea plantations has caused soil C-N imbalance, leading to ecological issues. Understanding soil C-N coupling under nitrogen loading is essential for sustainable management, yet the mechanisms remain unclear. This study examined C-N coupling in tea plantation soils under five fertilization regimes: no fertilization, chemical fertilizer, chemical + organic cake fertilizer, chemical + microbial fertilizer, and chemical + biochar. Fertilization mainly increased particulate organic carbon (POC) and inorganic nitrogen, driven by changes in bacterial community composition and function. Mixed fertilization treatments enhanced the association between bacterial communities and soil properties, increasing ecological complexity without altering overall trends. Fungal communities had a minor influence on soil C-N dynamics. Microbial necromass carbon (MNC) and microbial carbon pump (MCP) efficacy, representing long-term carbon storage potential, showed minimal responses to short-term fertilization. However, the microbial necromass accumulation coefficient (NAC) was nitrogen-sensitive, indicating short-term responses. PLS-PM analysis revealed consistent C-N coupling across the treatments, where soil nitrogen influenced carbon through enzyme activity and MCP, while bacterial communities directly affected carbon storage. These findings provide insights for precise soil C-N management and sustainable tea plantation practices under climate change.