Study On Moderate Grazing Utilization Of Rehabilitated Grassland Based On Ecological Stoichiometric Characteristics In Loess Plateau

With the implementation of the“Grain for Green”programs,a large area of rehabilitated grassland has been formed in the Loess Plateau.Its future development and sustainable management have become an important issue concerned by all sectors of society in the post conversion period.Grazing is one of the main use types of grassland.Moderate grazing can promote the succession of grassland plant communities,improve soil quality and enhance the stability and sustainability of ecosystem.Ecological chemometrics,which studies ecological processes and ecological functions based on element ratio,provides a new perspective and method for the study of ecosystem stability and sustainable development.Therefore,taking rehabilitated grassland in the Loess Plateau as the object,this study analysed the nutrients and ecological stoichiometric characteristics of plants-litter-biocrusts and subsoil of rehabilitated grassland under different grazing intensity,and revealed the influencing factors of grazing on the ecological stoichiometric characteristics of plant-litter-biocrusts and subsoil,which was combined with fixed sample plot experiment and field investigation,laboratory analysis and mathematical statistics.The study could provide scientific basis and technical support for the moderate utilization and sustainable development of the rehabilitated grassland in the Loess Plateau.The results are as follows:（1）When the grazing intensity was higher than 6.9 goat·ha^-1 in the study area,the coverage and biomass of vegetation and litter decreased significantly.Under short-term grazing,when the grazing intensity was higher than 6.7 goat·ha^-1,the coverage of vegetation,litter and biocrusts decreased significantly by 32.23%,32.55%and 18.00%respectively.Compared with no grazing,the vegetation biomass decreased significantly under each grazing intensity,the biomass of litter,cyanobacterial increased first and then decreased with the increasing grazing intensity,the moss biomass did not change significantly.Under long-term grazing,there was no significant difference in biocrusts coverage.Compared with no grazing,when the grazing intensity was greater than 3.3 goat·ha^-1,the vegetation coverage significantly reduced by 37.90%～45.30%.When the grazing intensity was higher than 6.9 goat·ha^-1,the litter coverage,the vegetation biomass,the litter biomass,cyanobacteria and moss biomass decreases by 43.40%～61.70%,54.24%～65.38%,16.74%～61.70%,44.79%and 69.54%,respectively.（2）When the grazing intensity in the study area was higher than 6.9 goat·ha^-1,the aboveground parts N content increased significantly,while the C and P contents had no significant effect;Grazing had no significant effect on the C,N and P contents in the underground parts of plants and litter.Under short-term grazing,there was no significant difference in the C and P contents of aboveground parts and the C,N and P contents of litter under different grazing intensities.When the grazing intensity was higher than 4.2 goat·ha^-1,the N content of aboveground parts of plants increased significantly by 29.32%～37.19%.Under long-term grazing,there was no significant difference in the C and P contents of aboveground parts and litter,the C,N and P contents of underground parts of plants under different grazing intensities.When the grazing intensity was higher than 6.9 goat·ha^-1,the N content in the aboveground parts of the plants increased significantly by 29.32%～37.19%.（3）In the study area,grazing had no significant effect on the N and P contents in biocrusts.However,when the grazing intensity was higher than 6.9 goat·ha^-1,the C contents in the biocrust layer and 0～2cm soil layer were significantly lower than no grazing.Under short-term grazing,the N and P contents in the biocrust layer and 0～2cm soil layer did not change under each grazing intensity.When the grazing intensity was higher than 6.7 goat·ha^-1,the C content in biocrusts decreased by 29.88%.Under long-term grazing,the N and P contents in the biocrust layer and 0～2cm soil layer did not change significantly under each grazing intensitity.When the grazing intensity was higher than 6.9 goat·ha^-1,the C content in the biocrust layer and 0～2cm soil layer significantly decreased by 98.33%and 84.14%,respectively.（4）In the study area,grazing had no significant effect on the N:P and C:P in the aboveground parts of the plants,the C:N,N:P and C:P in the underground parts of the plants and litter.When the grazing intensity was higher than 6.9 goat·ha^-1,the C:N in the aboveground parts of the plants decreased significantly.Under short-term grazing,the N:P and C:P in the aboveground parts of the plants,the C:N,N:P and C:P in litter did not change significantly under each grazing intensity.When the grazing intensity was higher than 6.7 goat·ha^-1,the C:N in the aboveground parts of plants significantly decreased by 28.75%～36.84%.Under long-term grazing,the N:P and C:P in the aboveground parts of the plants,the C:N,N:P and C:P in the belowground parts of the plants and litter did not change significantly under each grazing intensity.When the grazing intensity was higher than 6.9goat·ha^-1,the C:N in the aboveground parts of the plants significantly reduced by 24.04%～39.14%.（5）In the study area,grazing had no significant effect on the C:N in biocrust soil.When the long-term grazing intensity was higher than 6.9 goat·ha^-1,the N:P and C:P in the biocrust layer and 0～2cm soil layer significantly decreased.Short-term grazing had no significant effect on the C:N,N:P and C:P in the biocrust layer and 0～2 cm soil layer.Under long-term grazing,the C:N in biocrust layer and 0～2cm soil layer did not decrease significantly.When the grazing intensity was higher than 6.9 goat·ha^-1,the N:P and C:P decreased by 49.6%,49.9%,respectively.In conclusion,in the study area,when the grazing intensity was higher than 6.9goat·ha^-1,the C:N in plants and litter significantly reduced,and the C contents and C:N and C:P in the biocrust soil also significantly reduced,which may be beneficial to alleviate soil N and P constraints to a certain extent.However,comprehensively considering the surface characteristics of vegetation,litter,biocrusts and soil physical and chemical properties,moderate grazing could maintain nutrient cycling and ecological function in the rehabilitated grasslands in the study area.The above results provide technical support for moderate utilization of rehabilitated grasslands.