Soil microbial necromass carbon (C) is a crucial component of the soil organic C pool. The impact of both straw mulching treatments and years on the soil microbial necromass C accumulation remains unclear. We investigated factors driving soil microbial necromass C accumulation and its role in improving yield by analyzing the dynamic response of microbial necromass C, total organic C (TOC) and available nutrients, genes encoding carbohydrate-degrading enzymes and fruit yield of citrus under different straw types of mulching (wheat, rice, oilseed rape, no mulch) from 2019 to 2022. Annual rainfall was the main factor affecting the soil bacterial necromass C (BNC) accumulation. Straw mulching treatments were the main factor affecting the soil fungal necromass C (FNC) accumulation. Increased annual rainfall and high soil moisture levels hindered the soil microbial necromass C accumulation, especially BNC. No correlation was found between BNC and the relative abundance of genes encoding peptidoglycan (bacteria-derived biomass) degrading enzymes. Decreased relative abundance of genes encoding chitin (fungal-derived biomass) degrading enzymes, particularly GH18, favored the accumulation of FNC. Actinomycetes were the most significant contributors of the GH18 gene among microbial phyla. Moreover, oilseed rape and rice mulching treatments reduced the relative abundance of genes encoding enzymes degrading chitin. Microbial necromass C, especially BNC, was key for sustaining TOC, supplying nutrients, and enhancing citrus fruit yield. Our results provide new information for optimizing straw mulch type and application time in citrus orchards to improve soil microbial necromass accumulation.

土壤微生物死体碳（C）是土壤有机碳库的重要组成部分。秸秆覆盖处理和年份对土壤微生物坏死物碳积累的影响仍不清楚。通过分析不同秸秆类型下微生物死体碳、总有机碳（TOC）和速效养分的动态响应、碳水化合物降解酶编码基因以及柑橘果实产量的动态响应，探讨土壤微生物死体碳积累的驱动因素及其对增产的作用。 2019年至2022年覆盖（小麦、水稻、油菜、无覆盖）的情况。年降雨量是影响土壤细菌坏死物C（BNC）积累的主要因素。秸秆覆盖处理是影响土壤真菌坏死物C（FNC）积累的主要因素。年降雨量增加和土壤湿度高阻碍了土壤微生物坏死物C的积累，尤其是BNC。未发现 BNC 与编码肽聚糖（细菌来源的生物质）降解酶的基因的相对丰度之间存在相关性。编码几丁质（真菌来源的生物质）降解酶的基因（尤其是 GH18）的相对丰度降低，有利于 FNC 的积累。放线菌是微生物门中 GH18 基因最重要的贡献者。此外，油菜和水稻覆盖处理降低了编码降解甲壳素的酶的基因的相对丰度。微生物坏死物 C，尤其是 BNC，是维持 TOC、提供营养和提高柑橘类水果产量的关键。我们的研究结果为优化柑橘园秸秆覆盖类型和施用时间以改善土壤微生物坏死物积累提供了新信息。