高寒草地灌丛化对土壤团聚体生态化学计量学及酶活性的影响

草地灌丛化是影响土壤有机碳库储量的驱动因子之一。本研究以川西高寒灌丛化和未灌丛化草地为对象，分析团聚体内有机碳、全氮、全磷、全钾含量、蔗糖酶、脲酶、磷酸酶、过氧化氢酶、蛋白酶和β-D葡萄糖苷酶活性及生态化学计量比特征。结果表明：1）有机碳、全氮和全磷主要富集在0.053~0.25 mm团聚体内，灌丛化降低了团聚体内生源物质含量。2）灌丛化后团聚体内C/N、C/P和N/P均呈增加趋势，且C/N最大值出现在>2 mm团聚体中，而C/P和N/P的最大值均出现在0.053~0.25 mm团聚体中，最小值分别出现在<0.002 mm和0.002~0.053 mm团聚体中（P>0.05）。3）灌丛化草地和未灌丛化草地土壤酶活性呈>0.25 mm团聚体内富集，灌丛化后土壤各粒径团聚体中蔗糖酶活性增加、而蛋白酶和磷酸酶活性降低。4）脲酶和β-D葡萄糖苷酶在灌丛化草地和未灌丛化草地中均与土壤有机碳和全氮含量呈正相关关系，蔗糖酶和过氧化氢酶与全钾含量呈正相关关系，蛋白酶和磷酸酶与全磷含量呈正相关关系。该区域土壤生源物质主要固存于大团聚体内，而大团聚体易被外界干扰破碎，可见灌丛化现象不利于该研究区有机碳的长期固存。

Effects of shrub encroachment on soil aggregate ecological stoichiometry and enzyme activity in alpine grassland

Shrub encroachment is one of the key factors affecting soil organic carbon storage in alpine grassland. In this study， we compared soil properties with and without shrub encroachment in grasslands at the eastern margin of Qinghai-Tibetan Plateau. Soil parameters measured included the contents of organic carbon， total nitrogen， total phosphorus， and total potassium， and activities of sucrase， urease， phosphatase， catalase， protease and glucosidase， as well as the ecological stoichiometry characteristics of soil aggregates of various sizes. Our results showed that： 1） The contents of organic carbon， total nitrogen and total phosphorus in different sized aggregates decreased after shrub encroachment and were higher in large aggregates （0.053-0.25 mm） in size. 2） The C∶N， C∶P and N∶P ratios in soil aggregates increased after shrub encroachment. The maximum C∶N ratio was observed in the >2 mm aggregates. The maximum C∶P and N∶P ratios were observed in the 0.053-0.25 mm aggregates， and the minimum values were observed in <0.002 mm and 0.002-0.053 mm aggregates（P>0.05）. 3） Urease， sucrase， phosphatase， catalase and β-D glucosidase activities were elevated mainly in >0.25 mm aggregates at grassland and shrub encroachment. After shrub encroachment， sucrase activity increased， while the protease and phosphatase activities decreased. 4） Urease and β-D glucosidase activities were positively correlated with soil organic carbon and total nitrogen， sucrase and catalase activities were positively correlated with total potassium contents， and protease and phosphatase activities were positively correlated with total phosphorus. Soil biogenic materials are mainly concentrated in large aggregates in this region. However， large aggregates are easily broken by external interference， which shows that the phenomenon of shrub encroachment is not conducive to the sequestration of organic carbon in this area.