Abstract: To investigate the influence of heavy metal content in different degraded gradient alpine meadow soil on soil nutrient and enzyme activity,this experiment selected four different degradation gradient of alpine grasslands,namely no-degradation grassland (ND),light degradation grassland (LD),moderate degradation grassland (MD) and severe degradation grassland (HD) in three-river source area as the research objects. Alpine meadow soil samples of 0~10 cm,10~20 cm and 20~30 cm were taken respectively,and the soil physical and chemical properties,including total nitrogen,total phosphorus,total potassium and total carbon,etc.,enzyme activity(urease,invertase and amylase,protease,cellulase,phosphatase,catalase and polyphenol oxidase) and heavy metal content (copper Cu lead,chromium,Cr,Pb,Zn zinc and cadmium Cd) were measured and analyzed. The results showed that the physical and chemical properties,enzyme activity and heavy metal content of soil firstly decreased,then increased and then decreased with the severity of the degradation of alpine grasslands. In terms of soil physical and chemical properties,the total carbon,nitrate nitrogen and pH of grassland in the 0~10 cm soil layer,total nitrogen,nitrate nitrogen,carbon and pH in the 10~20 cm soil layer,and total nitrogen and carbon in the 20~30 cm soil layer with different degrees of degradation were significantly different (P<0.05). Among the soil enzymes,urease,sucrase,catalase and polyphenol oxidase were significantly different in the soils with different degrees of degradation from 0~10 cm,and urease,sucrase,amylase,catalase and polyphenol oxidase in the soils with different degrees of degradation from 10~20 cm and from 20~30 cm (P<0.05). Regarding the contents of heavy metal elements in soil,Cu,Cd,Zn and Cu,Cr and Cd in soil from 0~10 cm and 10~20 cm were significantly different (P<0.05). The same degradation has the enrichment tendency of different soil layers. Correlation analysis showed that the contents of 5 heavy metals were significantly correlated with soil physical and chemical properties,soil urease,sucrase,polyphenol oxidase and catalase (P<0.05). According to the calculation of soil pollution load index,all degraded gradient soils are moderately polluted with heavy metals. In summary,the changes of soil physics,enzyme activity and heavy metal content in different degraded grassland were analyzed,so as to provide references for soil health,sustainable resource utilization and soil degradation prevention in alpine grassland of Three Rivers Source.

Key words: Three-river headwaters region, Alpine steppe, Soil nutrients, Soil enzymes, Soil heavy metals

摘要： 为了探讨不同退化梯度高寒草地土壤重金属含量对土壤养分和酶活性的影响，本试验以三江源区玛多县周边高寒草地未退化（Non-degraded grassland，ND）、轻度退化（Light degraded grassland，LD）、中度退化（Moderate degraded grassland，MD）以及重度退化（Heavy degraded grassland，HD）4种不同退化梯度为研究对象，分别采取高寒草地0~10 cm、10~20 cm和20~30 cm的土样，对土壤理化性质（全氮、全磷、全钾和全碳等）、酶活性（脲酶、蔗糖酶、淀粉酶、蛋白酶、纤维素酶、磷酸酶、过氧化氢酶、多酚氧化酶）和重金属含量（铜Cu、铬Cr、铅Pb、锌Zn和镉Cd）进行测定和分析。试验结果表明，土壤理化性质、酶活性和重金属含量随着高寒草地退化程度的加剧呈先降低后上升再降低的趋势。土壤理化性质中，不同退化程度草地0~10 cm土层土壤全碳、硝态氮和pH差异显著（P<0.05）；10~20 cm土层土壤全氮、硝态氮、全碳和pH差异显著（P<0.05）；20~30 cm土层土壤全氮和全碳差异显著（P<0.05）。土壤酶中，不同退化程度草地0~10 cm土层土壤脲酶、蔗糖酶、过氧化氢酶和多酚氧化酶，差异显著（P<0.05）；10~20 cm和20~30 cm土层土壤脲酶、蔗糖酶、淀粉酶、过氧化氢酶和多酚氧化酶差异显著（P<0.05）。土壤重金属元素含量中，不同退化程度草地0~10 cm和10~20 cm土层土壤Cu，Cd，Zn以及20~30 cm土层Cu，Cr，Cd差异显著（P<0.05）。同一退化程度随土层加深重金属含量具富集趋势。相关性分析显示5种重金属含量与土壤理化性质和土壤脲酶、蔗糖酶、多酚氧化酶以及过氧化氢酶显著相关（P<0.05）。根据土壤污染负荷指数法计算，各退化梯度土壤均属于重金属中度污染。综上所述，本试验分析了不同退化草地土壤物理变化、酶活性变化及重金属含量变化，可为三江源高寒草地土壤健康、资源可持续利用、防止土壤退化提供参考。

关键词: 三江源, 高寒草原, 土壤养分, 土壤酶, 土壤重金属