土壤-牧草氮素供需状况变化对高寒草甸植被演替与草地退化的影响

Effects of nitrogen supply and demand status of soil and herbage system on vegetation succession and grassland degradation in alpine meadow

在中国科学院海北高寒草甸生态系统定位站 ,选取处于不同退化阶段的具有典型代表意义的草甸草场为研究对象 ,通过对其土壤氮素矿化补给能力、牧草对氮素的需求量的研究 ,探讨土壤 牧草氮素供需状况变化对高寒草甸植被演替与草地退化的影响。结果表明 ,在牧草生长季 5～ 8月 ,高寒草甸土壤的氮素矿化补给量为 15 86 g·m-2 ,而随着高寒草甸退化程度的加重 ,植物群落中优势种群由禾草演替为禾草 +苔草 +嵩草、嵩草至杂类草 ,其牧草生长需要的总氮量分别为 2 2 86、2 4 87、37 3、14 96g·m-2 ,只有在杂类草草甸阶段 ,其牧草生长对氮素的需求才与其土壤氮素供求相适配 ,可见养分是高寒草甸植被演替与草场退化的重要驱动因子之一。

Four typical pastures which represented different degradation stage of alpine meadow were selected at Haibei station of alpine meadow ecosystem.Thus,the studies on soil nitrogen supply ability due to its mineralization and herbages' demand for nitrogen were conducted.Consequently,effects of nitrogen supply and demand status of soil and herbage system on vegetation succession and grassland degradation in alpine meadow was discussed.The results showed that during the herbages growing period from May to August,through nitrogen mineralization,soil supplied 15.86 g·m -2.However,with the aggravation of grassland degradation,the dominate population in the communities was succeessed fromGramineae to Gramineae and Cyperaceae,and then to Kobresia,and forb.During the process of succession,the herbages' total demands for nitrogen were 22.86,24.87,37.3 and 14.96g·m -2,respectively.Only at the stage of soil nitrogen supply can meet the demands of herbage's growth.Therefore,nutrient is one of the most important driving factors that lead to vegetation succession and pasture degradation in alpine meadow region.