Abstract The mobilization of soil nutrients bound in organic matter is largely mediated by enzymes derived from plants, soil microorganisms and animal residues. Land-use change alters important soil characteristics that may affect the activities of soil enzymes. However, mechanistic understanding of how land use and management practices influence the catalytic properties of enzymes in top- and subsoil are still scarce, especially in African ecosystems. We linked catalytic properties i.e. substrate affinity constant (Km) and maximum reaction rate (Vmax), determined by Michaelis–Menten kinetics, to a set of environmental and microbial variables in the soils of a land-use sequence (6 ecosystems) ranging from natural forests to agricultural fields at Mt. Kilimanjaro. The sensitivity of Km and Vmax of four extracellular hydrolytical enzymes, β-galactosidase, cellobiohydrolase, phosphatase and chitinase to changing environmental conditions were tested by fluorogenic substrates in topsoils and subsoils. The β-galactosidase activity increased with increasing soil depth. Other extracellular enzyme (cellobiohydrolase, phosphatase and chitinase) activities decreased with depth. The affinity of enzymes to substrates was higher in soils of natural compared to agricultural ecosystems: i.e. higher under forests than under cropland. The activity of β-galactosidase, cellobiohydrolase and chitinase enzyme were highest in lower mountain forest and grassland (less disturbed ecosystems). This indicated that changes in land use and management practice not only affects enzyme activity but also controls enzyme kinetics (Km and Ka) thus pointing towards the expression of different enzyme systems. Therefore, we concluded that anthropogenic activities result in alteration of C and nutrient cycling by affecting microbial activities and enzymes catalytic properties.

中文翻译：

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土地利用和海拔对山地土壤酶功能特性的影响。乞力马扎罗

摘要 结合在有机质中的土壤养分的动员主要由来自植物、土壤微生物和动物残留物的酶介导。土地利用变化改变了可能影响土壤酶活性的重要土壤特征。然而，关于土地利用和管理实践如何影响表层和底土中酶的催化特性的机制理解仍然很少，尤其是在非洲生态系统中。我们将催化特性，即由 Michaelis-Menten 动力学确定的底物亲和常数 (Km) 和最大反应速率 (Vmax) 与土地利用序列（6 个生态系统）的土壤中的一组环境和微生物变量联系起来，范围从自然从森林到山的农田 乞力马扎罗。四种细胞外水解酶的 Km 和 Vmax 的敏感性，通过表土和底土中的荧光底物测试了 β-半乳糖苷酶、纤维二糖水解酶、磷酸酶和几丁质酶对不断变化的环境条件的影响。β-半乳糖苷酶活性随着土壤深度的增加而增加。其他细胞外酶（纤维二糖水解酶、磷酸酶和几丁质酶）活性随深度降低。与农业生态系统相比，天然土壤中酶对底物的亲和力更高：即森林下比农田下更高。β-半乳糖苷酶、纤维二糖水解酶和几丁质酶的活性在低山森林和草原（较少受干扰的生态系统）中最高。这表明土地利用和管理实践的变化不仅影响酶活性，而且控制酶动力学（Km 和 Ka），从而指向不同酶系统的表达。