Effects Of Different Grazing Intensities On Grassland Soil Respiration And Its Components In The Agro-pastoral Ecotone Of Northern Shanxi

Soil respiration is a key component of soil carbon dynamics,and grazing is a major use of grassland.Assessing the impact on grazing intensity on soil respiration in grassland ecosystems is critical to understanding the changes in grassland ecosystem carbon source/sink functions under human disturbance.In order to investigate the response to grassland soil respiration and its components to different grazing intensities,an experimental study was conducted in the agro-pastoral ecotone of northern Shanxi relied on the Youyu Loess Plateau grassland ecosystem research station.Four treatments were set up: ungrazing,light grazing(2.35 sheep unit·hm-2·growing season),moderate grazing(4.80 sheep unit·hm-2·growing season)and heavy grazing(7.35 sheep unit·hm-2·growth season).Soil heterotrophic respiration and total respiration were distinguished with deep-shallow PVC collars method,which were determined by automatic soil carbon flux measurement system LI-8100 A during the growing season(May to September)from 2018 to 2020,while also monitored the non-biological factors like soil temperature and soil moisture and the biological factors like above-ground and underground biomass were also monitored.The seasonal dynamics of soil respiration and its components were analyzed,and the effects of grazing intensity and related factors of them were explored.The main results are as follows:1.Grazing intensity had a significant effect on soil heterotrophic respiration.Compared with ungrazing,light grazing significantly reduced soil heterotrophic respiration by 17.7%(P<0.05).However,grazing intensity had no significant effect on soil autotrophic respiration.The average contribution of soil heterotrophic respiration to soil total respiration were 53.18%~72.81%,and the grazing intensity had a significant impact on it.The contribution to soil heterotrophic respiration to soil total respiration under light and moderate grazing was significantly lower than that under ungrazing and heavy grazing(P<0.05).2.The rate of soil respiration and its components were regulated by soil temperature,showing obvious seasonal dynamics(P<0.001),and the peak occurred in the vigorous growing every year.Soil temperature sensitivity(Q10 value)ranged from 1.05 to 3.40.The temperature sensitivity of soil heterotrophic respiration was significantly higher than that of soil autotrophic respiration(P<0.05).Different grazing intensities had no significant effect on the temperature sensitivity of soil respiration.3.Structural equation model could explain 45% and 25% of the change in soil heterotrophic respiration and autotrophic respiration,respectively.Soil temperature was the key regulator of different grazing intensity on soil heterotrophic respiration(β=0.37),and above-ground biomass was the key regulator of soil autotrophic respiration(β=0.32).In summary,in the grassland ecosystem of the agro-pastoral ecotone of northern Shanxi,grazing intensity influenced total soil respiration by affecting soil heterotrophic respiration,and soil temperature was the main limiting factor.