摘要:土壤胞外酶够将大分子有机质分解成可以被微生物利用的小分子化合物，在土壤有机质分解与转化过程中起着重要的作用。因此，土壤中酶促反应往往成为陆地生态系统中土壤有机质分解的限速步骤。然而，土壤酶活性的地理分布格局，尤其是其随着不同海拔和坡向的分布特征和驱动机制，仍不明确。为探讨土壤胞外酶的空间分布特征及影响因素，我们沿海拔梯度（2980-5120 m）在青藏高原唐古拉山的南北坡选取了6个样点，测定了参与碳、氮、磷循环的6种水解酶的活性和土壤理化性质，并结合植被和气象数据进行分析。结果显示，随海拔梯度的升高，年均温度（MAT）、土壤碳氮比（C：N）降低，年均降水量（MAP）、紫外线辐射（UV）、归一化植被指数（NDVI）、土壤碳含量（TC）、土壤氮含量（TN）升高；南坡的MAP、UV、NDVI、TC、TN显著高于北坡，而C：N显著低于北坡。不同类型的土壤胞外酶对海拔和坡向的响应不同，碳获取酶α-葡萄糖苷酶（AG）、β-葡萄糖苷酶（BG）、β-木糖苷酶（BX），以及氮获取酶N-乙酰-氨基葡萄糖苷酶（NAG）活性均随海拔梯度的升高而升高，且都在南坡显著高于北坡；磷获取酶酸性磷酸酶（AP）和氮获取酶亮氨酸氨基肽酶（LAP）活性在不同海拔和坡向的分布上并没有显著差异。模型平均和相对重要性分析表明，NDVI、RB和TC是驱动碳获取酶（AG、BG、BX）活性随海拔梯度和坡向分布格局的主要因子；NDVI是驱动参与氮获取酶（NAG）活性变化的主要因子。我们的研究结果表明，不同海拔和坡向上植被和土壤特征的差异驱动了土壤胞外酶活性的空间分布，从而可能对碳循环和养分循环产生不同的影响，为预测土壤胞外酶的空间地理格局提供了科学依据。



Abstract:Soil extracellular enzymes play a key role in the degradation and turnover of soil organic matter since they depolymerize large organic matter into low molecular compounds assimilated by microbes. Enzymatic reactions are the rate-limiting steps in soil organic matter decomposition and have profound impacts on biogeochemical cycle in terrestrial ecosystems. However, we know little about the spatial distribution of soil enzyme activities and the underlying mechanisms. To explore the spatial distribution and the driving factors of soil extracellular enzymes along the altitude and aspect, we selected six sites along the altitude gradients on the windward and leeward slopes of the Tanggula Mountains in the Qinghai-Tibet Plateau, respectively. We measured six types soil extracellular enzymes activities which involved in carbon, nitrogen and phosphorus cycles of soil, soil moisture (SM), soil carbon content (TC), and soil nitrogen content (TN). We investigated plant root biomass (RB), obtained normalized difference vegetation index (NDVI) as aboveground biomass index, mean annual temperature (MAT), mean annual precipitation (MAP), and ultraviolet radiation (UV) as climate factors. The results showed that MAT, and C:N decreased, whereas MAP, UV, NDVI, TC, TN increased along the increasing altitude. MAP, UV, NDVI, TC, and TN were significantly higher, while C:N were lower on the windward slope than those on the leeward slope. The specific extracellular enzymes differed in their activity responses to altitudes and aspects. Specifically, the activities of C-acquiring exoenzymes α-glucosidase (AG), β-glucosidase (BG), β-xylosidase (BX), and N-acquiring exoenzyme N-acetyl-glucosaminidase (NAG) all increased along increasing altitude gradient. In addition, the activities of AG, BG, BX, and NAG were significantly higher on the windward slope than on the leeward slope. However, neither altitude nor aspect had significant effects on P-acquiring exoenzymes acid phosphatase (AP) and N-acquiring exoenzymes leucine aminopeptidase (LAP). Our further analysis of model average and relative importance suggested that the NDVI, RB and TC were the main factors driving the changes in activities of C-acquiring exoenzymes (AG, BG, BX) along altitude gradient and aspect. However, the changes in activities of N-acquiring exoenzymes (NAG) was predominantly only driven by NDVI. Overall, this finding indicate that climate and soil characteristics drive the spatial distribution of various extracellular enzyme activity in soils at different altitudes and aspects, regulating carbon and nitrogen cycling. This study provides justification for the prediction of the spatial patterns of soil extracellular enzyme activities.





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