Abstract The depolymerization of organic proteinaceous compounds is a critical step of nitrogen (N) cycling in many agroecosystems, but our understanding of this process and the overall effect on N cycling is still limited. We have investigated long-term (11 years) impacts of tillage practices (traditional tillage, TT vs. no-tillage, NT) and Ca-amendment on the activity of soil casein protease (an enzyme degrading high-molecular weight proteinaceous compounds), N-α-benzoyl- l -argininamide protease (BAA) (targeting low-molecular weight compounds) and β-glucosidase in relation with organic matter pools and the composition of extractable soil organic matter. While the adoption of NT increased the β-glucosidase activity and the total and extractable organic C contents in the soil, only casein protease was increased by NT in the 0–5 cm soil layer. In contrast, Ca-amended plots showed a 50% higher casein protease and a lower BAA protease activity while β-glucosidase was unaffected. The decrease of BAA protease activity could be due to the reduction of easily extractable glomalin-related soil protein caused by Ca-amendment and highlights the tight relations between soil protease and glomalin. The imbalance in enzymatic activity may result in an accumulation of intermediate metabolic products (i.e. monomers and amino acids), therefore involving reduced mineral N losses and/or changes in N acquisition preferences by plants. Our results further suggest that the combination of NT and Ca-amendment application does not have synergic effects on the studied enzyme activities. In addition, the effects of agronomic practices were limited to the upper soil layers because of soil stratification caused by NT and the higher effect of Ca-amendment in topsoil. Further targeted studies are needed to elucidate the impact of agronomic practices on N losses and on the N use by soil microbes and plants.

中文翻译：

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免耕加钙对地中海农田土壤蛋白酶和β-葡萄糖苷酶活性的长期影响

摘要 有机蛋白质化合物的解聚是许多农业生态系统中氮（N）循环的关键步骤，但我们对该过程的了解以及对氮循环的整体影响仍然有限。我们研究了耕作做法（传统耕作，TT 与免耕，NT）和 Ca 修正对土壤酪蛋白蛋白酶（一种降解高分子量蛋白质化合物的酶）活性的长期（11 年）影响， N-α-苯甲酰-l-精氨酰胺蛋白酶 (BAA)（靶向低分子量化合物）和 β-葡萄糖苷酶与有机物质库和可提取土壤有机物质的组成有关。虽然 NT 的采用增加了 β-葡萄糖苷酶活性和土壤中总的和可提取的有机碳含量，但在 0-5 cm 土层中，NT 仅增加了酪蛋白蛋白酶。相比之下，Ca 修正图显示酪蛋白蛋白酶高 50%，BAA 蛋白酶活性较低，而 β-葡萄糖苷酶不受影响。BAA 蛋白酶活性的降低可能是由于 Ca 修正引起的易提取的球藻蛋白相关土壤蛋白质的减少，突出了土壤蛋白酶与球藻蛋白之间的紧密关系。酶活性的不平衡可能导致中间代谢产物（即单体和氨基酸）的积累，因此涉及减少矿物氮损失和/或植物对氮获取偏好的变化。我们的结果进一步表明 NT 和 Ca 修正应用的组合对所研究的酶活性没有协同作用。此外，由于 NT 引起的土壤分层和表土中 Ca 修正的更高影响，农艺实践的影响仅限于上层土层。需要进一步有针对性的研究来阐明农艺实践对氮损失和土壤微生物和植物氮利用的影响。