The Effects Of Different Managements On Plant Community,soil Stoichiometry And Microbial Community In Bare Land Alpine Sown Grassland Of The Yellow River Source Region

The effective management of alpine sown grassland is vital to the restoration in alpine grassland.Establishing sown grassland is a method used widely to treat heavily degraded alpine grassland.However,the managements used after establishing is important for the restoration of ecosystem fuctions and productivity.In recent decades,the area of sown grassland in Qinghai-Tibetan plateau has increased dramatically,facing the problem of sown grassland succession.Finding the proper techniques and practices to tackle the sown grassland is crucial for the maintenance of ecosystem productivity and ecosystem services,which is meaningful for the further establishment and management of the sown grassland in the future.There conducted three manipulative field experiments testing the effects of mowing（Mowing,Control）,fertilizing using three forms of nitrogen（Urine: 10 g N m-2 yr-1,Ammonium: 10 g N m-2 yr-1,Nitrate: 10 g N m-2 yr-1,Control: No fertilization）,and removing Ligularia virgaurea in four diferent densities（D1: 0 plant/m2;D2: 15 plant/m2;D3: 30 plant/m2,Control: 45 plant/m2）in a 5-year alpine sown grassland in Guinan county,Qinghai province.Comparing plant community,soil characteristics,microbial community at scale of functional group and community,I studied:（1）the effects of different managements on sown grassland community composition,productivity,and diverisity indices,（2）the effects of different managements on plant functional group stoichiometry characteristics and soil stoichiometry characteristics,（3）the relationship between plant functional groups and soil on stoichiometry characteristics.These experiments provided practical evidences for long-term management of alpine sown grassland.The results showed that:（1）Compared to Y0（2018-before treatments）,both mowing and fertilizing can significantly influence the plant community compositon（P < 0.05）,and compared with Control,mowing also had effect on plant community composition（P < 0.05）.Compared to Y0,both mowing and fertilizing siginificantly decreased the Pielou evenness index of plant community（P < 0.05）.No evidence was found of changes in plant community composition,diversity indices under different removal densities of L.virgaurea.Mowing siginificantly reduced the residue biomass（P < 0.05）.All treatments did not effect biomass of different functional groups,aboveground biomass,belowground biomass in both soil layers（0-10 cm,10-20cm）.Fertilizing with different forms of nitrogen significantly influenced the grass biomass nitrogen and forbs biomass carbon（P < 0.05）.However,no evidence of change on plant functional group stoichiometry characteristics was found under mowing treatment.（2）Mowing had siginificant influence on soil total nitrogen and N:P ratio（P < 0.05）.The range of soil C:N ratio is between 9.24±1.21 to 11.42±0.84,which indicated the nitrogen constraint in this site.Fertilizing with different forms of nitrogen had siginificant effects on soil electrical conductivity,total phosphorus,NO3-N,microbial biomass carbon,microbial biomass nitrogen（P < 0.05）.Removal of L.virgaurea had siginificantly influenced soil total nitrogen,total potassium,total organic carbon,and C:P ratio both in 0-10 cm and 10-20 cm soil layers（P < 0.05）.（3）After mowing treatment,there was no correlation between root nutrients（C,N,P）and soil nutrients（C,N,P）.In fertilazition treatments regardless of nitrogen forms,root phosphorus content of 0-10 cm soil layer positively correlated with soil total phosphorus of 10-20cm（P < 0.05）.Both soil C:P ratio and soil N:P ratio in 10-20 cm soil layers also had positive correlation with root C:P ratio and soil N:P ratio in repective soil layers under fertilization treatments.（4）Removal of L.virgaurea had siginificant effects on composition and abundance of bacteria and fungi.The relative abandances of these bacterial genera,Bacillus,Arthrobacter,norank_f<sub>67-14,Bradyrhizobium,norank_f<sub>Xanthobacteraceae,norank_f<sub>JG30-KF-CM45,Microvirga significantly changed under different removal densities of L.virgaurea（P < 0.05）.Besides,the relative abandances of these fungal genera,unclassified_p<sub>Ascomycota,Mortierella,Tetracladium,Solicoccozyma,unclassified_f<sub>Chaetomiaceae also significantly changed under different removal densities of L.virgaurea（P < 0.05）.Finally,mowing,fertilization and removal of L.virgaurea all had negligible effect on aboveground plant community,but displayed sufficient effects on soil physicochemical characteristics.Meanwhile,removal of L.virgaurea demonstrated siginificant effects on bacterial and fungal microbial community.Consequently,there needs some further studies of different managements before their long-term application on alpine sown grassland.