贺兰山东坡不同海拔梯度土壤酶化学计量特征

土壤胞外酶是生物地球化学循环的主要参与者，与微生物的代谢需求和养分供应密切相关。然而，对干旱区山地生态系统沿海拔梯度土壤微生物养分限制状况及其驱动因素尚不清楚。基于此，以贺兰山海拔1300-2700m范围内7个海拔梯度的土壤为研究对象，揭示贺兰山土壤理化性质、胞外酶活性及微生物养分限制的海拔分布格局，分析影响微生物养分限制的驱动因素。结果表明：随着海拔梯度的升高，土壤含水率（SWC）和有机碳（SOC）含量逐渐增加，容重（BD）和pH整体呈现逐渐降低的趋势。海拔显著影响土壤胞外酶活性，五种参与土壤碳（C）、氮（N）、磷（P）循环的酶活性随着海拔的升高整体呈现逐渐上升的变化趋势，总体表现出中低海拔酶活性较低，高海拔酶活性较高。胞外酶矢量分析显示，矢量长度在中低海拔处较高，而矢量角度则在高海拔处较高，表明贺兰山土壤微生物在中低海拔和高海拔分别具有相对较强的C和P限制。土壤含水率、容重、C、N、P含量与土壤胞外酶活性及其化学计量比显著相关，是调控土壤胞外酶活性随海拔变化的主要因子，说明胞外酶在旱区山地生态系统土壤物质循环过程中具有重要的作用。该研究结果对揭示土壤微生物和胞外酶之间养分元素循环的耦合机理，为深入探讨贺兰山森林生态系统物质循环和不同海拔梯度植被有效管理提供科学依据。

Responses of soil enzyme activities and their stoichiometric characteristics to different altitude on the eastern slope of Helan Mountain

Soil extracellular enzymes are closely related to the metabolic requirements and nutrient supply of microorganisms and are major players in biogeochemical cycles. However, the status of soil microbial nutrient limitation and its drivers in mountain ecosystems along the elevation gradient are not well understood in the arid regions. Taking the soils of seven elevation gradients from 1300 m to 2700 m in Helan Mountain as the research object, this paper revealed the elevation distribution patterns of soil physical and chemical properties, extracellular enzyme activities and microbial nutrient limitation, and analyzed the driving factors affecting microbial nutrient limitation. The results showed that with the increase of altitude gradient, the soil water content (SWC) and soil organic carbon (SOC) gradually increased, the bulk density (BD) and pH gradually decreased. Altitude had significant effect on soil extracellular enzyme activities, and the activities of five enzymes involved in soil carbon (C), nitrogen (N) and phosphorus (P) cycles gradually increased with the increase of altitude. Vector analysis of extracellular enzymes showed that the vector length was higher at mid and low altitudes, while the vector angle was higher at high altitudes, indicating that soil microorganisms in Helan Mountain had relatively strong C limitation at mid and low altitudes, and P limitation at high altitude. Soil moisture content, bulk density, C, N and P contents were significantly correlated with soil extracellular enzyme activities and their stoichiometric ratios, which were main factors regulating soil extracellular enzyme activities with altitude, indicating that the extracellular enzymes played an important role in soil material cycling in arid mountainous ecosystem. The study results provide a scientific basis for revealing the coupling mechanism of nutrient element cycling between soil microorganisms and extracellular enzymes, and for further exploring the material cycling of the forest ecosystem and the effective management of vegetation at different altitude gradients in Helan Mountain.