Assessment Of Grassland Desertification In Zoige Basin

Grassland ecosystem is the largest terrestrial ecosystem in China.Grassland ecosystems are fragile for being to susceptible to human activities,and global climate and environmental to cause grassland degradation.With the degradation of grassland ecosystems,a series of ecological problems,such as the fragmentation of grassland ecosystems,changes in plant community diversity,deteriorates in the structure and function of grassland ecosystems,and the decline or even loss of ecological functions necessary to maintain ecological processes will occur.In this study,the Zoige basin was selected as the research object,and the NDVI was selected to evaluate the grassland desertification in the Zoige area for 15 years(2003-2017);the typical desertification land was selected and classed into 9 desertification grades according to the degree of natural degradation.By analyzing the relationship between soil physicochemical properties and plants by correlation matrix analysis,variance test,linear relationship fitting,RDA and SEM,the relationship between above-ground and below-ground biomass of desertification gradients and environmental factors and the key factors affecting the distribution of plant biomass were determined,and the key ecological mechanisms for grassland desertification were identified.The following conclusions can be drawn from the study:(1)Compared with 2003-2010,grassland changes in the four counties of Hongyuan,Zoige,Maqu and Ngawa counties during 2010-2017 all showed an increase in degraded areas and a decrease in grassland restoration area.Arima model predicts that the average NDVI value of Ngawa County,Hongyuan County,Maqu County,and Zoige County will increase significantly from 2018 to 2027.(2)With the increased desertification degree,the Simpson index,Margalef index were decreasing,and the Pielous index increased,the species species decrease,and the dominance is obvious.AGB and BGB at soil depth of 0-30 cm decreased with increasing desertification.The explanatory powers of soil bulk densities(SBD),soil organic carbon(SOC),soil available nitrogen(SAN),soil available phosphorus(SAP),soil total nitrogen(STN),and soil total phosphorus(STP)on AGB were 0.237,0.442,0.433,0.302,0.511,and 0.244,respectively;the explanatory power for BGB was 0.298,0.436,0.487,0.163,0.467 and 0.345 respectively.(3)The AGB-BGB in desertified land follows the hypotheses of allometric allocation;the pH value of soil increases with the increasing degree of desertification.Under the stress of desertification gradient,R/S decreases with the increase of SBD.(4)The total soil nutrient content of SOC,STC,SAN,STN,SAP,and STP had a 0.703 impact on the trade-off between AGB and BGB,while the total influence of SBD and SWC on the tradeoff was-0.074.In a continuous desertification gradient,soil nutrient content is the main factor that changes the above-ground biomass,below-ground biomass and its distribution.The results of this study can provide a theoretical basis for effectively curbing grassland degradation.Moreover,by analyzing the linkage mechanism between grassland degradation and key influencing factors,grassland ecological restoration and control measures for degraded grassland can be rationally formulated to protect the grassland ecological environment and achieve rational allocation and sustainable use of resources.