The kinetics of extracellular enzymes produced by soil microorganisms regulate soil organic matter decomposition and other ecosystem functions. Atmospheric nitrogen (N) deposition creates a soil environment with elevated reactive N, which is expected to affect the kinetic parameters (V_max and K_m) of hydrolytic and polyphenol oxidative enzymes, as well as soil microbial respiration. We measured the V_max and K_m of seven soil hydrolytic enzymes and polyphenol oxidase (PPO), as well as soil microbial respiration and physiochemical properties, in a temperate steppe after 15 years of multi-level N addition treatments. As the N addition increased, the V_max of most carbon (C)-degrading and N-degrading hydrolytic enzymes decreased, and this was associated with a decline in soil pH. In contrast, the V_max of acid phosphatase (AP) increased with increasing N addition. Higher N addition was associated with lower K_m of most hydrolytic enzymes, expect for AP and β-xylosidase (BX). There was a quadratic relationship between N addition and the V_max and K_m of PPO, which reached a maximum with the addition of 8 g ;N m⁻² y⁻¹, and decreased at higher N addition levels. Structural equation modeling indicated that the decline in soil microbial respiration with increasing N deposition was directly mediated by the BG kinetics, due to the fact N-induced acidification negatively impacted the V_max and K_m of BG. Our empirical data on soil enzyme (i.e., V_max, K_m) and its relationship with microbial respiration should be useful for modelling how microbes and substrates interact to regulate soil carbon cycling under N enrichment.

土壤微生物产生的细胞外酶的动力学调节土壤有机物的分解和其他生态系统功能。大气中的氮（N）沉积会产生活性N升高的土壤环境，这有望影响水解酶和多酚氧化酶的动力学参数（V _max和K _m），以及土壤微生物的呼吸作用。我们在经过15年的多级氮添加处理后，在温带草原中测量了7种土壤水解酶和多酚氧化酶（PPO）的V _max和K _m，以及土壤微生物的呼吸作用和理化特性。随着N的增加，V _max大部分降解碳（C）和降解N的水解酶都减少了，这与土壤pH值下降有关。相反，酸性磷酸酶（AP）的V _max随氮添加量的增加而增加。N的增加与大多数水解酶的K _m降低有关，对于AP和β-木糖苷酶（BX）而言是期望的。N的添加与PPO的V _max和K _m之间存在二次关系，在添加8 g时达到最大值，N m ^-2 y ^-1，并在较高的氮添加水平下降低。结构方程模型表明，土壤微生物呼吸作用随着氮沉降的增加而直接由BG动力学介导，这是由于N诱导的酸化对BG的V _max和K _m产生了负面影响。我们关于土壤酶（即V _max，K _m）及其与微生物呼吸的关系的经验数据对于模拟微生物和底物如何相互作用以调节氮富集下土壤碳循环应该是有用的。