Effects of slope aspect on soil enzyme activity and microbial nutrient limitation in subalpine region of wes-tern Sichuan, China.

Exploring the resource limitation of soil microbial metabolism is essential to understand ecosystem functions and processes. However, the spatially divergent patterns and drivers of soil microbial nutrient limitation cha-racteristics in montane ecosystems at small scales, especially at the slope aspect scale, are still unclear. In this study, we measured soil enzyme activities involved in carbon (C), nitrogen (N) and phosphorus (P) cycle and quantified the microbial nutrient limitations by enzyme stoichiometry in two representative mountain sites in subalpine region of western Sichuan, including the sunny and shady slopes with different vegetation types (shrubland and forest, respectively) in Miyaluo of Lixian County, and with the same vegetation type (shrubland) in Yakexia of Heishui County. The results showed that soil enzyme activities and their stoichiometric ratios were significantly different between slope aspects in Miyaluo, while the differences were not significant in Yakexia. The stoichiometry ratio of C-, N- and P-acquiring enzymes on the sunny slope of Miyaluo was 1:0.96:0.92, approaching the 1:1:1 ratio at the global scale, but deviated from 1:1:1 on the shady slope of Miyaluo (1:1.39:0.75) and the different slopes of Yakexia (1:1.09:1.35). There was no significant difference in vector length between slope aspects at both sites, indicating no significant effect of slope aspect on the microbial C limitation. The vector angle was significantly higher on the sunny slope (43.6°) than that on the shady slope (28.7°) in Miyaluo, suggesting that the microorganisms were mainly N-limited. Partial least squares path model showed that the vector angle was mainly directly influenced by the soil nutrient ratios. The vector angle ranged from 50.3° to 51.4°, and did not differ between slope aspects in Yakexia. Therefore, differences in vegetation types between slope aspects drove variations in soil enzyme activity and microbial nutrient limitation through soil properties. It would provide a scientific basis for predicting the spatial pattern of soil enzyme activity and microbial nutrient limitation.研究土壤微生物代谢的资源限制对理解生态系统的功能和过程至关重要。然而,山地生态系统土壤微生物养分限制特征在小尺度,尤其是坡向上的空间分异格局和驱动因素仍不清楚。本研究在具有代表性的川西亚高山理县米亚罗选取了植被类型不同的阳坡(灌丛)和阴坡(森林),在黑水县雅克夏选取了植被类型相同的阳坡和阴坡(灌丛),测定了参与土壤碳氮磷循环的酶活性,通过酶化学计量比量化了微生物的养分限制。结果表明: 不同坡向间土壤酶活性及其化学计量比在米亚罗差异显著,而在雅克夏则不显著。米亚罗阳坡土壤碳氮磷获取酶化学计量比为1∶0.96∶0.92,接近于全球尺度上的1∶1∶1,米亚罗阴坡(1∶1.39∶0.75)和雅克夏不同坡向(1∶1.09∶1.35)则偏离于1∶1∶1。两个地点坡向间矢量长度无显著差异,表明坡向对微生物碳相对限制无显著影响。米亚罗阳坡矢量角度(43.6°)显著高于阴坡(28.7°),微生物主要受氮的相对限制,偏最小二乘路径模型显示,矢量角度主要受土壤养分计量比的直接影响。而雅克夏不同坡向间矢量角度介于50.3°~51.4°,且坡向间无显著差异。坡向间植被类型的不同通过土壤性质驱动了土壤酶活性及微生物养分限制的变异,为预测土壤酶活性及微生物养分限制的空间格局提供了科学依据。.