Response Of Alpine Grassland Ecosystem To Grazing And Fencing In Tibetan Plateau

The Qinghai-Tibet Plateau is not only an important characteristic animal husbandry base in China,but also an important influence on the climate of the northern hemisphere.It is also the birthplace of many mother rivers in China and neighboring countries,and has a great impact on the ecological environment and social economy in the east and southwest of China.85% of the total area of the Qinghai-Tibet Plateau is alpine grassland,which is the main pasture for Tibetan sheep and yak grazing.Alpine grassland plays an important role in ecological services such as climate regulation,diversity protection and water and soil conservation.However,due to the impact of global climate change and human activities,especially the long-term unreasonable grazing patterns,the alpine grasslands on the Qinghai-Tibet Plateau have been seriously degraded.The result of the cooperative change of vegetation-soil system is the concrete manifestation of alpine grassland degradation.Reversing grassland degradation is an important goal for grassland management and a challenge for restoration technology.In order to explore the grassland degradation of the Qinghai-Tibet Plateau and its response to grazing and fencing,we collected 129 research points on degradation,grazing and fencing.In this paper,alpine grassland of Qinghai-Tibet Plateau was taken as the research area to study the change characteristics of vegetation productivity,community characteristics and soil physicochemical properties under different conditions such as grazing intensities,degradation gradient and fenced-off years.The results showed that :(1)with the increase of grazing intensity,above-ground biomass decreased continually.In addition,we found that moderate grazing had a significant positive effect on the below-ground biomass,increasing by 5.38%.The effect of grazing time on above-ground and below-ground biomass was similar to that of grazing intensity.In contrast,light and heavy grazing had no significant effect on below-ground biomass.Light and moderate grazing treatments had the least effect on the total biomass,while heavy grazing treatments significantly reduced the total biomass.There was no significant effect on total biomass under moderate grazing,possibly because the decrease in above-ground biomass offset the increase in subsurface biomass.The results of moderate grazing provide evidence for the biomass transfer hypothesis.There was a significant increase in the below-ground biomass under moderate and 1-2 years grazing,which supported the grazing optimization hypothesis.(2)the main mechanisms that lead to the increase of below-ground biomass in moderate grazing are the compensatory growth of plant individuals,the trend of plant community dwarfing,the significant increase of species richness and the change of soil microbial community caused by grazing.(3)under different degradation gradients,both above and below-ground biomass of vegetation decreased,and soil characteristics showed a deteriorating trend.Especially in severely degraded grassland,above-ground biomass and belowground biomass,species richness and species evenness is not degraded grassland were significantly reduced by 42.44%,60.64%,21.08% and 8.36%,the soil water content,organic carbon,total nitrogen and total phosphorus is not same degraded grassland were significantly decreased by 33.57%,45.75%,22.70% and 11.23%,and the soil bulk density was significantly increased by 12.12%(P < 0.05).In terms of effect ratio,vegetation biomass was significantly positively correlated with the main properties of soil(organic carbon,total nitrogen and total phosphorus),indicating that vegetation productivity and soil properties influenced each other during grassland degradation,and carbon content loss was very serious compared with nitrogen and phosphorus content.Phosphorus content in alpine grasslands may be a limiting element for plant growth and development.(4)in terms of the years of fencing,short-term fencing(1-4 years)increased the above-ground biomass,Shannon-Weiner index,soil organic carbon,soil total nitrogen and soil total phosphorus content of alpine meadow.However,there was no significant change in above-ground biomass,below-ground biomass,vegetation coverage,Shannon-Weiner index,soil organic carbon,soil total nitrogen and soil total phosphorus in the alpine meadow after 5-8 years or 8 years of fencing.In relatively dry alpine grasslands,1-4 years of fencing significantly increased aboveground biomass and vegetation coverage.The 8 years of fencing increased the vegetation coverage and the number of Shannon-Weiner index.Therefore,time is a very important factor for ecological recovery.Short-term fencing can improve species diversity and vegetation productivity,while long-term fencing has no obvious positive impact on the ecosystem and may even lead to the loss of species diversity in alpine meadow.(5)the increase of soil carbon content is accompanied by the increase of soil nitrogen content,indicating that nitrogen may be the key factor supporting the increase of soil carbon content in the short-term fencing.However,insufficient supply of nitrogen may be the main reason for the late decline in carbon sequestration capacity.In our study,the community structure stabilized after 8 years of fencing.Our study suggests that moderate grazing and short or medium term fencing(no more than 8 years)are the best grassland restoration measures and management model for alpine grassland,and the research results can provide theoretical reference and guidance for the sustainable development of alpine grassland ecosystem on the Qinghai-Tibet Plateau.