Exogenous nitrogen (N) input is a key factor affecting litter decomposition. However, we have limited understanding on how anthropogenic N deposition affects the kinetics and thermodynamics of enzymes involved in litter decomposition. To understand how N enrichment influences litter decomposition, we conducted a field N-addition experiment with Castanopsis chinensis (CC) and Schima superba (SS) leaf litter. We examined microbial community composition, activities of hydrolases and oxidative enzymes, and hydrolase kinetics and thermodynamics. The litter mass remaining after 18 months of decomposition in N-addition plots was 1.9–2.3 and 1–1.3 times higher than control for CC and SS, respectively. During the early stage of litter decomposition, N addition increased hydrolase activities involved in carbon (C) and N mineralization for both litter types. N addition slowed CC litter mass loss, and reduced the activities of lignolytic enzymes and catalytic efficiency ( V max / K m ) of hydrolases in the later stage (9–18 months) of decomposition. N addition had minimal effect on the activation energy (Ea) of enzymes. Our study identifies how enzyme kinetics regulate litter decomposition under N fertilization, and lignin enrichment as decomposition progresses due to microbial N mining effect limits the accessibility of lignin-encrusted structural carbohydrates to hydrolases, which subsequently decreases the energy source of the entire microbial community for enzyme production.

中文翻译：

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真菌生物量的变化以及水解酶和氧化酶的活性解释了凋落物分解对氮添加的不同反应

外源氮 (N) 输入是影响凋落物分解的关键因素。然而，我们对人为 N 沉积如何影响参与凋落物分解的酶的动力学和热力学了解有限。为了解富氮如何影响凋落物分解，我们对栲 (CC) 和黑木 (SS) 落叶进行了田间加氮实验。我们检查了微生物群落组成、水解酶和氧化酶的活性，以及​​水解酶动力学和热力学。在添加氮的地块中分解 18 个月后剩余的垃圾质量分别比 CC 和 SS 的对照高 1.9-2.3 倍和 1-1.3 倍。在凋落物分解的早期阶段，N 添加增加了参与碳 (C) 和 N 矿化两种凋落物类型的水解酶活性。N添加减缓了CC凋落物质量损失，并降低了分解后期（9-18个月）木质分解酶的活性和水解酶的催化效率（V max / K m ）。N 添加对酶的活化能 (Ea) 的影响很小。我们的研究确定了酶动力学如何在施氮下调节凋落物分解，并且由于微生物 N 开采效应导致分解过程中的木质素富集限制了木质素包裹的结构碳水化合物对水解酶的可及性，从而降低了整个微生物群落酶的能量来源生产。N 添加对酶的活化能 (Ea) 的影响很小。我们的研究确定了酶动力学如何在施氮下调节凋落物分解，并且由于微生物 N 开采效应导致分解过程中木质素的富集限制了木质素包裹的结构碳水化合物对水解酶的可及性，从而降低了整个微生物群落酶的能量来源生产。N 添加对酶的活化能 (Ea) 的影响很小。我们的研究确定了酶动力学如何在施氮下调节凋落物分解，并且由于微生物 N 开采效应导致分解过程中的木质素富集限制了木质素包裹的结构碳水化合物对水解酶的可及性，从而降低了整个微生物群落酶的能量来源生产。