Soil extracellular enzyme activities reflect the microbial nutrient demand by microorganisms and can be strongly affected by land use change. However, how soil N-hydrolyzing enzymes and soil extracellular enzyme stoichiometry (EES) respond to land use change remains unclear. Here, we explored seasonal variations in β-1,4-N-acetyl glucosaminidase and leucine aminopeptidase activities and EES under afforested land (woodland and shrubland), cropland, and uncultivated land for better understanding microbial metabolism around the Danjiangkou Reservoir area. Both afforested and cropland soils averaged higher N-hydrolyzing enzyme and specific enzyme activities [i.e., enzyme activities per unit of soil organic nitrogen (SON)] compared to the uncultivated soils, indicating fast N turnover rates after afforestation and cultivation. Higher N-hydrolyzing enzyme activities under afforestation and cultivation could be attributed to increasing soil organic carbon and soil organic nitrogen contents. All land use types were generally restricted by nutrients limitation than C demand as mean soil ecoenzymatic C:N:P ratios deviated from 1:1:1. However, afforestation and cultivation r|esulted in greater C demand and alleviate nutrient limitation for soil microorganisms with higher ecoenzymatic C:N ratios, C:P ratios, and vector lengths. In addition, all land use types were restricted by P than N limitation with ecoenzymatic N:P ratios less than 1 and vector angle >45°, among which afforestation increased P limitation and cultivation alleviated P limitation for microbes compared with uncultivated land. Overall, our results provide insight into mechanisms of soil microbial metabolic limitation regulated by soil N-hydrolyzing enzyme activity and EES under global land use change.

中文翻译：

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亚热带土地利用变化后土壤氮水解酶活性和化学计量学

土壤细胞外酶活性反映了微生物对微生物养分的需求，并且会受到土地利用变化的强烈影响。然而，土壤氮水解酶和土壤细胞外酶化学计量（EES）如何响应土地利用变化仍不清楚。在这里，我们探索了绿地（林地和灌木地）、农田和未开垦土地下 β-1,4-N-乙酰氨基葡萄糖苷酶和亮氨酸氨基肽酶活性和 EES 的季节性变化，以更好地了解丹江口水库区周围的微生物代谢。与未开垦的土壤相比，造林土壤和农田土壤均具有更高的氮水解酶和特定酶活性 [即每单位土壤有机氮 (SON) 的酶活性]，表明植树造林和耕作后氮的周转率很快。造林和栽培下较高的氮水解酶活性可归因于土壤有机碳和土壤有机氮含量的增加。由于平均土壤生态酶 C:N:P 比率偏离 1:1:1，所有土地利用类型通常都受养分限制而不是 C 需求。然而，植树造林和栽培导致了更大的 C 需求并减轻了土壤微生物对具有更高生态酶 C:N 比、C:P 比和载体长度的养分限制。此外，所有土地利用类型都受到P比N限制的限制，生态酶N:P比小于1且矢量角>45°，其中与未开垦的土地相比，植树造林增加了P限制，种植减轻了P限制。总体，