Soil enzymes play important roles in soil C and nutrient cycling. However, the effects of N addition on soil enzyme kinetics and the underlying mechanisms remain unclear. Thus, we aimed to determine the effects of short-term N addition on the soil properties, microbial properties, maximum reaction rate (, which is attained at saturating substrate concentrations), and Michaelis constant (, where a high indicates low substrate affinity) of microbial C- (β-1,4-glucosidase and cellobiohydrolase), N- (β-1,4-N-acetylglucosaminidase and L-leucine aminopeptidase), and P-degrading (acid phosphatase and alkaline phosphatase) enzymes in subtropical coniferous () and broadleaf () forests. In the broadleaf forest, N addition increased the and substrate-binding affinities (decline in ) of C- and P-degrading enzymes by triggering a P deficiency response in microorganisms (i.e., increased microbial biomass N:P ratio). These findings indicate that the soil enzyme kinetics followed the optimal foraging strategy in response to N addition. Moreover, N addition reduced the proportion of complex organic molecules in dissolved organic matter (DOM; e.g., reduced abundance of humic-like fluorophores and humification index), suggesting that N addition increased soil DOM quality and thus increased the affinities of C-degrading enzymes. N addition increased the abundance of and but reduced the abundance of and , indicating a shift in microbial community toward efficient P acquisition. N addition affected bacterial composition and thus indirectly influenced N- and P-degrading enzymes. In the coniferous forest, N addition significantly increased the of C-degrading enzymes but did not change other enzyme kinetics, which could be partly attributed to the unchanged N availability and microbial properties. Collectively, our findings provide insights into the relationship between enzyme kinetics, DOM quality, and microbial properties, which are important for predicting soil nutrient cycling and parameterizing models of C cycling under N deposition.

中文翻译：

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短期施氮条件下土壤溶解有机质质量和细菌群落组成调节水解酶的底物结合亲和力

土壤酶在土壤碳和养分循环中发挥着重要作用。然而，氮添加对土壤酶动力学的影响及其潜在机制仍不清楚。因此，我们的目的是确定短期施氮对土壤特性、微生物特性、最大反应速率（在饱和底物浓度下达到）和米氏常数（高表示底物亲和力低）的影响。亚热带针叶树中的微生物 C-（β-1,4-葡萄糖苷酶和纤维二糖水解酶）、N-（β-1,4-N-乙酰氨基葡萄糖苷酶和 L-亮氨酸氨基肽酶）和 P-降解酶（酸性磷酸酶和碱性磷酸酶） ）和阔叶林（ ）。在阔叶林中，氮的添加通过触发微生物中的磷缺乏反应（即增加微生物生物量氮磷比）来增加碳和磷降解酶的底物结合亲和力（下降）。这些发现表明，土壤酶动力学遵循响应氮添加的最佳觅食策略。此外，氮的添加降低了溶解有机质中复杂有机分子的比例（DOM；例如，腐殖质类荧光团的丰度和腐殖化指数降低），这表明氮的添加提高了土壤DOM质量，从而提高了C降解酶的亲和力。氮的添加增加了 和 的丰度，但降低了 和 的丰度，表明微生物群落向高效获取磷的方向转变。氮的添加影响细菌组成，从而间接影响氮和磷降解酶。在针叶林中，氮的添加显着增加了碳降解酶的活性，但没有改变其他酶的动力学，这可能部分归因于氮的有效性和微生物特性没有改变。总的来说，我们的研究结果提供了对酶动力学、DOM 质量和微生物特性之间关系的见解，这对于预测土壤养分循环和氮沉降下碳循环的参数化模型非常重要。