Root exudates can significantly modify microbial activity and soil organic matter (SOM) mineralization. However, how root exudates and their C/N stoichiometric ratios control rice field (paddy) soil C mineralization is poorly understood. This study used a mixture of glucose, oxalic acid, and alanine as root exudate mimics for three C/N stoichiometric ratios (CN6, CN10, and CN80) to explore the underlying mechanisms involved in SOM mineralization. The input of root exudates enhanced CO₂ emissions by 1.8–2.3-fold that of soil with only C additions (C-only). Artificial root exudates with low C/N ratios (CN6 and CN10) increased the metabolic quotient (qCO₂) by 12% over those with higher stoichiometric ratios (CN80 and C-only), suggesting a relatively high energy demand for microorganisms to acquire organic N from SOM by increasing N-hydrolase production. The increase of stoichiometric ratios of C- to N-hydrolase [β-1,4-glucosidase to β-1,4-N-acetyl glucosaminidase (NAG)] promoted SOM degradation compared to those involved in organic C- and N-degradation, which had a significant positive correlation with qCO₂. The stoichiometric ratios of microbial biomass were positively correlated with C use efficiency, indicating root exudates with higher C/N ratios provide an undersupply of N for microorganisms that trigger the release of N-degrading extracellular enzymes. Our findings showed that the C/N stoichiometry of root exudates controlled SOM mineralization by affecting the specific response of the microbial biomass through the activity of C- and N-releasing extracellular enzymes to adjust the microbial C/N ratio.

中文翻译：

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低碳氮比的根系分泌物加速稻田土壤的二氧化碳排放

根系分泌物可以显着改变微生物活性和土壤有机质 (SOM) 矿化。然而，人们对根系分泌物及其 C/N 化学计量比如何控制稻田（稻田）土壤 C 矿化知之甚少。本研究使用葡萄糖、草酸和丙氨酸的混合物作为三种 C/N 化学计量比（CN6、CN10 和 CN80）的根分泌物模拟物，以探索 SOM 矿化的潜在机制。与仅添加 C（仅 C）的土壤相比，根系分泌物的输入使 CO ₂排放量增加了 1.8-2.3 倍。具有低 C/N 比（CN6 和 CN10）的人工牙根分泌物增加了代谢商（qCO ₂) 比化学计量比较高的那些（CN80 和 C-only）高 12%，这表明微生物通过增加 N-水解酶的产量从 SOM 中获取有机 N 的能量需求相对较高。与参与有机 C-和 N-降解的那些相比，C-与 N-水解酶 [β-1,4-葡萄糖苷酶与 β-1,4-N-乙酰氨基葡萄糖苷酶 (NAG)] 的化学计量比的增加促进了 SOM 降解, 与 qCO _{2呈显着正相关}. 微生物生物量的化学计量比与 C 利用效率呈正相关，表明具有较高 C/N 比的根系分泌物为触发 N 降解细胞外酶释放的微生物提供了 N 供应不足。我们的研究结果表明，根系分泌物的 C/N 化学计量通过影响微生物生物量的特定反应来控制 SOM 矿化，这是通过释放 C 和 N 的细胞外酶的活性来调节微生物 C/N 比。