Effects Of Different Grazing Intensities On Soil Multifunctionality In Typical Steppe

The study of ecosystem multifunctionality（EMF）is the hotspots for current ecological research.Soil multifunctionality（SMF）,one of important components of ecosystem multifunctionality,refers to their capacity to provide and maintain multiple ecological functions in parallel.At present,the research on soil multifunctionality more focuses on farmland and forest ecosystems,and yet few studies on soil multifunctionality in grassland ecosystems.Moderate grazing conduces to maintain and improve soil multifunctionality.In this study,we took the typical grassland in Inner Mongolia as the research area.Based on the data including aboveground biomass,belowground biomass,and species diversity,soil organic carbon,total soil nitrogen,total soil phosphorus,soil available nitrogen,soil available phosphorus,β-glucosidase,microbial biomass carbon and microbial biomass nitrogen,the multifunctionality indexes were then calculated to assess the effects of grazing intensities on soil carbon,nitrogen,phosphorus cycling and soil multifunctionality in typical steppe,revealing the biotic and abiotic drivers of soil multifunctionality.The main findings and conclusions are as follows:1.During the growing season,the average above-ground and below-ground biomass without grazing were 179.47 g/m² and 1175.34 g/m²,respectively.Light and moderate grazing reduced above-ground by 5.93%and 2.5%respectively,and the belowground biomass by 18.49%and 27.66%,respectively（P<0.05）.Heavy grazing significantly reduced aboveground and belowground biomass by 50.44%and 41.44%,respectively（P<0.05）.Total biomass decreased significantly with increasing grazing intensity（P<0.05）.Grazing intensity significantly increased the relative biomass of perennial bunchgrass（PB）and significantly decreased the relative biomass of perennial rhizome grass（PR）and perennial forbs（PF）（P<0.05）.2.Under the 0-30cm soil layer,with the increase of grazing intensity,the activities of total nitrogen（TN）and N-acetyl-β-D-glucosidase（NAG）decreased;total organic carbon（TOC）,total phosphorus（TP）,Ammonium nitrogen（NH₄⁺-N）,available phosphorus（AP）andβ-glucosidase（BG）,cellobiohydrolase（CBH）,leucine aminopeptidase（LAP）,alkaline phosphatase（ALP）)activity first increased and then decreased;nitrate nitrogen（NO₃^--N）and microbial biomass nitrogen（MBN）first decreased and then increased;microbial biomass carbon（MBC）showed an"N"-type change.There was no significant difference in TOC,CBH activity and MBN under different grazing treatments;compared with no grazing,light grazing significantly increased TP,NH+4-N,LAP activity and MBC,and ALP activity was the highest under light grazing,significantly higher than Heavy grazing;moderate grazing significantly increased AP;heavy grazing significantly decreased TN,BG activity,NAG activity,and significantly increased NO₃^--N（P<0.05）.3.Soil multifunctionality was divided into three individual functions related to the carbon cycle,nitrogen cycle,and phosphorus cycle.With the increase of grazing intensity,the soil multifunctional index and the above three single function indexes changed synergistically.Compared with no grazing,light grazing significantly increased soil multifunctional index,carbon cycle index,and phosphorus cycle index（P<0.05）;although there was no significant difference in nitrogen cycle index under light grazing and no grazing,it was significantly higher than that of heavy grazing;moderate grazing had the highest phosphorus cycle index,which was significantly higher than no grazing（P<0.05）.4.Increasing grazing intensity has a direct negative driving effect on soil multifunctionality,because grazing intensity has a significant negative effect on soil carbon cycle,and then grazing intensity indirectly drives soil multifunctionality by reducing belowground biomass and soil water content.Belowground biomass has a significant negative effect on soil multifunctionality,carbon cycle,and nitrogen cycle;the reduction in belowground biomass tends to increase soil conductivity,which in turn has a negative effect on soil carbon cycle.Grazing intensity significantly increased soil bulk density,which was not conducive to soil nitrogen cycle;higher soil water was beneficial to soil multifunctionality and soil phosphorus cycle.Belowground biomass and some soil physical properties have significant effects on soil multifunctionality,while biodiversity has no significant effect on soil multifunctionality.