青藏高原高山嵩草高寒草甸不同退化阶段植物群落与土壤养分

Plant community and soil nutrient of alpine meadow in different degradation stages on the Tibetan Plateau,China

选取西藏自治区拉萨市当雄县4块不同退化程度的高山嵩草高寒草甸,采用空间序列代替时间演替的方法,研究不同退化阶段高寒草甸的土壤理化性质和植物群落特征以及二者之间的相关关系。结果表明:不同退化阶段高寒草甸的土壤有机碳、全氮、速效磷、速效钾、铵态氮、硝态氮和含水量均随土壤退化程度加剧呈降低的趋势,而pH值呈现升高的趋势。中度退化草甸的植物群落高度、丰富度指数、多样性指数、均匀度指数最大。群落盖度、总生物量均为未退化草甸最大、重度退化草甸最小。随着草甸退化程度加剧,莎草科生物量及比例下降,豆科和杂类草生物量及比例增加,禾本科生物量及比例先增加后减小;草甸植物群落地上生物量与土壤有机碳、全氮、全磷含量和土壤含水量呈显著正相关,与土壤pH值呈显著负相关。随着草甸植被的退化,土壤退化加重,最终表现为草地生产力显著下降。

We examined soil physical and chemical properties and plant community characteristics of four Kobresia alpine meadows at different degradation stages in Damxung County,Lhasa City,Tibet Autonomous Region,China,with the method of spatial sequence instead of time succession.The results showed that soil organic carbon,total nitrogen,available phosphorus,available potassium,ammonium,nitrate,and water content showed a decreasing trend as the degree of soil degradation increased,while pH showed an increasing trend.Plant community height,richness,diversity index and evenness index of the moderately degraded meadow were the highest.Community coverage and total biomass were the largest in undegraded meadow and the smallest in the severely degraded meadow.As the degree of meadow degradation intensifies,the biomass and proportion of Cyperaceae decreased,the biomass and proportion of legumes and weeds increased,and the biomass and proportion of Gramineae first increased and then decreased.The aboveground biomass of meadow was significantly positively correlated with soil organic carbon content,total nitrogen content,total phosphorus content,and soil water content,and significantly negatively correlated with soil pH.With the vegetation degradation in meadow,soil degradation had worsened,which ultimately manifested as a significant decline in grassland productivity.