Impacts Of Different Restoration Years Of Returning Grazing Land To Grassland On Community Characteristics And Soil Nutrients Of Alpine Grassland In Maqu County

Alpine grassland is an important part of the vegetation on the Qinghai Tibetan Plateau.It plays an irreplaceable role in maintaining the environmental quality,ecological safety and sustainable development of animal husbandry.Due to the influence of human disturbance and global change,leading to grassland degradation,productivity decline and dysfunction of grassland ecosystem have become increasingly prominent,which have seriously affected and restricted its production and ecological service functions for a long time.It is a huge challenge for human beings that how to maintain the sustainable use of the natural ecosystem.The goverment has started the project of returning grazing land to grassland since 2003,which has effectively alleviating the degradation of natural grassland and become one of the effective technique for the restoration of degraded grassland.There were a lot of research work for natural grassland restoration in the process of returning farmland and grassland technique,but previous studies have focused on the ground vegetation changes,few studies have pointed to compare the influence of different years for returning farmland to grassland on grassland plant community.It is lack of dynamic data both the ground vegetation community and the underground soil process with synchronicity restoration.This study chooses the typical of extreme degraded natural alpine grassland as the research object in Maqu county on the eastern of Qinghai Tibetan Plateau.Based on the influence of different years of returning farmland to grassland on alpine grassland.Studied the effects of 5-year,10-year and 15-year restoration on the plant communities and soil properties of degraded alpine grassland,and predicted the optimal restoration period of extremely degraded alpine grassland.Which provided theoretical basis and technical support for the restoration and utilization of degraded grassland resources.The main results are as follows:(1)Returing grazing land to grassland significantly increased plant community diversity index,the ground biomass,species evenness index and dominance index of alpine grassland at the community level,and had obvious dependence on restoration years.It is mainly reflected the community characteristics gradually increased rapidly and became stable duration restoration.The first 5 years were determined as the rapid restoration stage,the 5-10 years as the buffer stage and the 15 years as the restoration and stability stage,respectively.(2)Returing grazing land to grassland significant changed the component of plant community in functional group level,and had obvious dependence on duration years.It is mainly reflected firstly from grasses and forbs co-dominant communities changed to sedges and leguminous co-dominant communities,and then to only the sedge was the dominant community,and finally to sedges and grasses were the co-dominant communities.It can be seen that the change of plant community function group is an important indicator to predict the restoration process of extremely degraded alpine grassland in this study.(3)Soil properties changes in the restoration process of degraded grassland.Returing grazing land to grassland significantly reduced soil p H,resulting in the transformation of soil from neutral to weakly acidic.It increased soil organic carbon and total nitrogen contents,and improved soil carbon fixation and nitrogen retention capacity.The content of total phosphorus,available phosphorus and available nitrogen were decreased in alpine grassland soil duration restoration years.Soil porosity was significantly reduced after returning grazing land to grassland,and the total soil porosity was much higher than the natural grassland background value after grassland restoration 15-year.This suggested that degraded grassland soil restoration is slower and more complex with the biological process compared with aboveground vegetation community.In conclusion,returning grazing land to grassland increased the productivity and diversity of plant communities and changed the composition of plant communities in degraded alpine grassland,which are mainly reflected in the replacement of community functions,but these changes were significantly dependent on the restoration years of degraded grasslands.Returning grazing land to grassland significantly reduced the soil p H.At the same time,it improved the contents of soil carbon and nitrogen,but reduced the soil available nutrient content and total soil porosity.This indicates that the process of underground soil restoration was longer and more complex for the biological process of degraded grassland.This study provided a new perspective for the studying of the degraded grassland restoration.The restoration project of degraded grassland should not only pay attention to the aboveground vegetation community,but also pay more attention to the underground ecological process.