Study On The Degradation Grade Divide And The Characteristics Of Carbon,Nitrogen And Phosphorus Of Alpine Grassland In Qilian Mountains

Scientific and accurate evaluation of the degradation degree and level of grassland ecosystem is an important basis for effective and high-quality ecological restoration of degraded grassland.The evaluation and determination of the degradation degree and level of grasslands in different regions and types are different,and the reasons that cause grassland degradation are also different,so the evaluation methods need to be improved according to the actual situation in order to provide guidance for the specific ecological restoration of degraded grasslands based on the local situations.The degradation of alpine grasslands in the Qilian Mountains is a serious problem,so the establishment of a classification method for the degradation level of alpine grasslands in the Qilian Mountains and the determination of the basic characteristics and restoration potential of different degradation levels are key scientific questions for the effective ecological restoration of degraded alpine grasslands in the Qilian Mountains currently.Based on this purpose,this study uses the typical degraded alpine grassland in the Qilian Mountains as the study object,and with the support of the comprehensive research work of the Second Qinghai-Tibet Plateau Scientific Research Expedition,the vegetation data and soil data obtained through field investigation and laboratory tests were used to construct the degradation index of the alpine grassland in the Qilian Mountains region through cluster analysis and principal component analysis,to determine the degradation grade and define the degradation level.The carbon,nitrogen and phosphorus characteristics of alpine grasslands with different degrees of degradation were clarified,and the influence factors of carbon,nitrogen and phosphorus stocks of degraded alpine grasslands were identified by using correlation analysis and multiple linear stepwise regression analysis.The main results of this study are as follows:(1)A more reliable alpine grassland degradation index(GDI)for the Qilian Mountains region was constructed optimally.By using the methods of cluster analysis and principal component analysis,seven indicators,including vegetation above-ground biomass,vegetation cover,proportion of good forage grass,proportion of degraded indicator species,soil p H,soil bulk and soil organic carbon,were selected as the main indicators for constructing the alpine grassland degradation index(GDI)in the Qilian Mountains region.The grassland degradation index(GDI)was optimized by calculating the relevant bases and weights of each main indicators,and calculated by weighted arithmetic average.The GDI of alpine grassland under different degradation levels were: non-degraded grassland: 0.75-1.00;lightly degraded grassland: 0.45-0.75;moderately degraded grassland: 0.25-0.45;and severely degraded grassland: ≤0.25.(2)Degradation of alpine grasslands in the Qilian Mountains significantly effected vegetation above-and below-ground relative indicators.Vegetation indicators such as vegetable above-ground biomass,vegetable below-ground biomass,and α-diversity of plant communities decreased significantly with the increased of degradation.Soil p H and soil bulk both showed an overall increased trend with the increased of degradation.Soil water content showed an overall decreased with the increased of degradation.(3)Degradation of alpine grassland in the Qilian Mountains significantly effected vegetation carbon,nitrogen and phosphorus stocks and soil carbon,nitrogen and phosphorus stocks.The carbon,nitrogen and phosphorus stocks of above-ground vegetation in the Qilian Mountains alpine grassland were significantly decreased with the increased of degradation.Soil total carbon stock,soil organic carbon stock and soil total nitrogen stock all showed a trend of first increased and then decreased with the increased of degradation.Soil total phosphorus stocks showed an overall increased trend with the increased of degradation.(4)The degraded alpine grasslands in the Qilian Mountains have considerable potential for carbon,nitrogen and phosphorus stocks restoration.If appropriate measures are taken for grassland restoration,the vegetation carbon,nitrogen and phosphorus stocks can be increased by 23.06 %,29.07 % and 21.05 %,the soil total carbon stocks and soil organic carbon stocks can be increased by 34.26 % and 49.73 %,and the soil total nitrogen stocks can be increased by 37.88 %,respectively.(5)Pearson correlation analysis and multiple linear stepwise regression analysis were used to identify the key factors influencing the above-and below-ground carbon,nitrogen and phosphorus stocks in the alpine grassland of Qilian Mountains.The results showed that vegetation above-ground biomass,vegetation below-ground biomass,soil bulk,soil p H,plant total carbon content,plant total phosphorus content,soil total carbon content,soil total nitrogen content and soil total phosphorus content were the key factors influencing above-ground and below-ground carbon,nitrogen and phosphorus stocks of alpine grasslands in the Qilian Mountains.In summary,this study optimized the construction of the Grassland Degradation Index(GDI)by quantitative ecological methods with the help of vegetation and soil related indicators of degraded alpine grasslands in the Qilian Mountains,and determined the characteristics of grasslands in different degradation grade,and analyzed the potential of grassland vegetation and soil carbon,nitrogen and phosphorus restoration.It is recommended that the results of this study could be used as an important basis for determining grassland degradation grades of grassland restoration and rehabilitation work in the future.