放牧胁迫下若尔盖高原沼泽退化特征及其影响因子

根据原生和退化沼泽水体、植被与土壤信息,将放牧胁迫下若尔盖高原沼泽划分为5个等级,即原始沼泽、轻度退化、中度退化、重度退化和极度退化沼泽,系统地研究了若尔盖高原沼泽的退化特征及其影响因子。沼泽退化特征表现为:退化沼泽水体总氮含量较高,硝态氮、总磷含量以及碱度、矿化度随沼泽退化程度加剧而上升。退化沼泽物种丰富度增加,群落组成和结构趋于多样化;群落水分生态型结构变化明显,中生植物逐渐取代沼生植物优势地位;沿沼泽退化梯度,植被演替速率降低。沼泽退化序列上,土壤含水率、毛管孔隙度、全氮含量降低,土壤容重、全磷和全钾含量上升;土壤垂直剖面上,退化沼泽较原始沼泽和轻度退化沼泽全量养分含量变化大,并且,全氮和全磷含量具有表聚性。退化沼泽环境指标PCA分析显示,沼泽退化受土壤养分和水分含量的影响较大。

Characteristics and influence factors of the swamp degradation under the stress of grazing in the Zoige Plateau

Swamp in the Zoige Plateau which was one of the five main pasture regions in China has been threatened by over-grazing for decades ever since 1960s. In this paper, typical degraded swamp was selected to figure out the main characteristics and critical influence factors under the stress of grazing. On the basis of its water,vegetation and soil information, the degraded swamp was classified into five stages, namely:primary swamp, lightly degradation, moderate degradation, severe degradation and extreme degradation. The degradation characteristics and their influence forces were discussed in this paper. The main characteristics of the degraded swamp water were: (1) TN was higher than normal, (2) TN, NO^-₃, TP, alkaline and the total dissolved solids increased along the degraded gradient,(3)the pH of water is between 8 to 9,(4) HCO^-₃ is the main contributor to the alkaline. The main changes of the degraded swamp vegetation were: (1) an increase of overall species abundance,(2) a decrease in the important values of helophyte, (3) an increase in the important values of mesophyte, (4) Potentilla ansrina replaced Carex muliensis and C. meyeriana as a dominant species in the community. By comparing the similarity between the communities of different degraded swamps,it was found that the rates of vegetation succession decreased along the swamp degraded gradient. The main changes of the degraded swamp soil along the degraded gradient were: (1)a decrease of soil water content, porosity, TN,(2)an increase of bulk density, TP, TK. The vertical changes of different nutrient contents in the soil profile of degraded swamps were complicated. On the whole, the content of TN and TP decreased along the soil depth gradient,and with the increase of depth,the influence of grazing on the content of TP decreased. In order to find out the main influence factors of swamp degradation under grazing, Principle components analysis (PCA) was employed in this paper. Five vegetation variables,eight water variables and six soil variables involved in PCA were simplified into three components which explained 50.77%, 30.50% and 16.72% of the total variables respectively. There was a significant positive relationship between PC1 and Shannon-Weiner index, the importance value of mesophyte as well as the total phosphorus content of soil and a negative relationship between PC1 and importance value of helophyte, Simpons index, water content as well as total nitrogen content of soil. The significant negative relationship between PC2 and pH of water was also observed. Principle components analysis indicated that water physical properties and nutrient of soil were the main driving factors that caused the swamp degradation in the Zoige Plateau. As the nineteen variables changed obviously along the degradation gradient,they were tried to be used to indicate the degree of swamp degradation. According to the three principle components gaining from PCA,a multiple linear regression model was developed based on the three factor scores which could be used to calculate the score of every kind of degraded swamp and it turned out to be useful in degraded swamp classification.