Effects Of Different Grazing Intensities On Carbon Fluxes In Semi-arid Grassland Ecosystems

Grassland is an important part of terrestrial ecosystem,with grazing is one of the most common and important utilization methods of grassland ecosystem,which plays an important role in carbon cycle of grassland ecosystem.Ecosystem carbon flux is an important index to evaluate carbon cycle and budget,which has an important impact on improving grassland productivity and maintaining global carbon balance.Therefore,it is of great theoretical significance to study the effects of different grazing intensities on ecosystem carbon flux for accurate assessment of ecosystem carbon budget.In this study,the semi-arid grassland ecosystem in Youyu Loess Plateau of Shanxi province was selected as the research object.Four different grazing intensities were set up,including ungrazing,light grazing,moderate grazing and heavy grazing.The net ecosystem carbon exchange and ecosystem respiration of grassland under different grazing intensities were dynamically monitored by static box method in the growing season of 2017-2019,and gross ecosystem photosynthetic rate was calculated.At the same time,soil temperature,soil moisture,soil bulk density,above-ground net primary productivity,below-ground net primary productivity,plant coverage and other indicators were monitored to explore the influence mechanisms of different grazing intensities on carbon flux of semi-arid grassland ecosystem in the short term.The results of three years experiments showed that:(1)Under short-term grazing intensity,the carbon flux of semi-arid grassland ecosystem showed a trend of first increasing and then decreasing during the whole growing season.Different grazing intensity only changed the peak value of grassland ecosystem carbon flux,but did not change its seasonal dynamic change.(2)The grassland ecosystem showed obvious "carbon sink" during the growing season.(3)Under different grazing intensities,NEE accumulation in growing season ranged from-82.34 to-48.76 g·C·m-2·a-1.(4)In the response mechanisms of soil temperature,soil moisture,soil bulk density,above-ground net primary productivity and below-ground net primary productivity,the study found that soil temperature and soil moisture were the main influencing factors of ecosystem carbon flux under different grazing intensities.And it also showed that the regulating effect of soil temperature was higher than soil moisture.