Labile carbon (C) inputs affect the soil carbon:nitrogen (C:N) ratio and microbial stoichiometric homeostasis, which control the intensity and direction of the priming effect (PE). Here, we clarified how soil microorganisms regulate enzyme production and PE to maintain the C:N stoichiometric balance. Specifically, we conducted an incubation experiment by adding ¹³C-labeled glucose to four long-term fertilized paddy soils: no fertilization; fertilization with mineral nitrogen, phosphorus, and potassium (NPK); NPK combined with straw; and NPK with manure (NPKM). After glucose addition, the dissolved organic carbon-to-ammonium (DOC:NH₄⁺) ratio (24–39) initially increased, but subsequently decreased after day 2 following glucose exhaustion. In parallel, the microbial C:N imbalance [(DOC:NH₄⁺):(microbial biomass C:microbial biomass N)] rapidly decreased from day 2 (4.6–7.2) to day 20 (<0.5). Thus, microorganisms became C limited after 20 days of incubation. Excess C, resulting from glucose addition, increased N-hydrolase (chitinase) production and N mining from soil organic matter (SOM) through positive PEs. However, C hydrolase (β-1,4-glucosidase and β-xylosidase) activity increased, while that of N hydrolase (chitinase) decreased, following glucose exhaustion. Consequently, the C:N microbial biomass ratio increased as the DOC:NH₄⁺ ratio decreased, leading to negative PEs. NPKM-fertilized soil had the largest cumulative PE (2.3% of soil organic carbon) because it had the highest microbial biomass and iron (Fe) reduction rate. Thus, this increased N mining from SOM maintained the microbial C:N stoichiometric balance. We concluded that soil microorganisms regulate C- and N-hydrolase production to control the intensity and direction of PE, maintaining the C:N stoichiometric balance in response to labile C inputs.

不稳定碳（C）的输入会影响土壤碳：氮（C：N）的比例和微生物化学计量的稳态，从而控制启动效应（PE）的强度和方向。在这里，我们阐明了土壤微生物如何调节酶的产生和PE以维持C：N的化学计量平衡。具体而言，我们通过向4种长期施肥的水稻土中添加¹³ C标记的葡萄糖进行了温育实验：用矿质氮，磷和钾（NPK）施肥；氮磷钾配秸秆; 和NPK肥料（NPKM）。添加葡萄糖后，溶解的有机碳-铵（DOC：NH ₄ ⁺）比率（24-39）开始上升，但在葡萄糖耗尽后的第2天之后下降。同时，微生物C：N不平衡[（DOC：NH ₄ ⁺）:(微生物生物量C：微生物生物量N）]从第2天（4.6-7.2）到第20天迅速减少（<0.5）。因此，温育20天后微生物变得C受限。葡萄糖添加导致的过量碳，增加了N-水解酶（几丁质酶）的产生以及通过阳性PE从土壤有机质（SOM）开采的氮。然而，葡萄糖耗尽后，C水解酶（β -1,4-葡萄糖苷酶和β-木糖苷酶）的活性增加，而N水解酶（几丁质酶）的活性降低。因此，随着DOC：NH ₄ ^+的增加，C：N微生物的生物量比增加。比率下降，导致PE变为负数。NPKM施肥的土壤具有最大的累积PE（占土壤有机碳的2.3％），因为它具有最高的微生物生物量和铁（Fe）还原率。因此，从SOM开采的增加的N含量保持了微生物C：N化学计量的平衡。我们得出结论，土壤微生物调节C和N水解酶的产生，以控制PE的强度和方向，响应不稳定的C输入，保持C：N的化学计量平衡。