Microorganisms regulate soil organic matter (SOM) formation through accumulation and decomposition of microbial necromass, which is directly and indirectly affected by elevated CO₂ and N fertilization. We investigated the role of microorganisms in SOM formation by analyzing ¹³C recovery in microorganisms and carbon pools in paddy soil under two CO₂ levels, with and without N fertilization, after continuous ¹³CO₂ labelling was stopped. Microbial turnover transferred ¹³C from living microbial biomass (determined by the decrease in phospholipid fatty acids) to necromass (determined by the increase in amino sugars). ¹³C incorporation in fungal living biomass and necromass was higher than that in bacteria. Bacterial turnover was faster than necromass decomposition, resulting in net necromass accumulation over time; fungal necromass remained stable. Elevated CO₂ and N fertilization increased the net accumulation of bacterial, but not fungal, necromass. CO₂ levels, but not N fertilization, significantly affected ¹³C incorporation in SOM pools. Elevated CO₂ increased ¹³C in particulate organic matter via the roots, and in the mineral-associated organic matter (MAOM) via bacterial, but not fungal, necromass. Overall, bacterial necromass plays a dominant role in the MAOM formation response to elevated CO₂ because bacteria are sensitive to elevated CO₂.

微生物通过微生物坏死物的积累和分解来调节土壤有机质（SOM）的形成，这直接或间接地受到CO ₂和N 施肥升高的影响。我们通过分析连续¹³ CO ₂标记停止后，在两种 CO _{2水平下（有和没有施氮肥）稻田土壤中微生物和碳库的}¹³ C 恢复情况，研究了微生物在 SOM 形成中的作用。微生物周转将¹³ C 从活微生物生物量（由磷脂脂肪酸的减少确定）转移到坏死物（由氨基糖的增加确定）。真菌活生物量和坏死物中的¹³ C 掺入量高于细菌中的 13 C 掺入量。细菌周转速度快于死灵物分解速度，导致死灵物随着时间的推移而净积累；真菌坏死物保持稳定。升高的CO ₂和N 施肥增加了细菌的净积累，但不增加真菌、坏死物的净积累。 CO ₂水平显着影响SOM 池中的¹³ C 掺入，但氮施肥没有影响。 CO ₂升高使根部颗粒有机物的温度升高¹³ °C，而细菌（而非真菌）坏死物使矿物质相关有机物 (MAOM) 的温度升高 13°C。总体而言，细菌坏死物在 CO ₂升高的 MAOM 形成反应中起主导作用，因为细菌对 CO ₂升高敏感。