Effects Of Different Mowing Intensities On Soil Srganic Carbon Dynamics Of Stipa Grandis Steppe

The dynamic change of soil organic carbon plays an important role in the global carbon cycle.Mowing is the most direct and most important utilization mode of grassland resources.For a long time,the impact of different mowing methods on the dynamic change of soil organic carbon is not very clear.This study took S.grandis steppe distributing in Xilingol League,Inner Mongolia as the research object,and the enclosure treatment and three different mowing intensity treatments(mowing once every two years,mowing once in a year and twice in a year)were set up.By investigating the composition of community species,above-ground and below-ground biomass,soil temperature and water content,as well as soil nutrients,the changes of community characteristics were clarified.Through determining the molecular composition of alkali-hydrolyzed lipids and lignin phenolic compounds in plants and soils,the specific biomarkers that could indicate aboveground and underground plant carbon in S.grandis steppe were screened out,and the contribution of plant-derived carbon to soil organic carbon and its degradation characteristics were analyzed.Also,by analyzing the correlation between the content of plant-derived carbon and soil organic carbon with the community characteristics,the influencing factors of soil organic carbon dynamics in S.grandis steppe under different mowing intensities were revealed.The research results can provide scientific management basis for the sustainable utilization and development of typical steppe in Inner Mongolia.The main conclusions results were as follows:1)Under the treatment of mowing once a year and twice a year,the dominance of S.grandis in the community decreased and Cleistogenes sibiricum gradually became constructive species of the community.The number of annual herb species increased under the treatment of mowing twice a year.Mowing significantly decreased the community aboveground and belowground biomass of S.grandis steppe.2)With the increase of enclosure years,the content of soil total organic carbon and total nitrogen in 0-10 cm soil layer increased significantly.There was no significant difference among the different treatments in each soil layer of 0-30 cm.Additionally,the content of soil total organic carbon and total nitrogen both decreased significantly with the increase of soil depth under different treatments.3)Under different treatments,there was no significant difference in the contribution of plant litter to soil organic carbon in the 0-30 cm soil layer,but the contribution of plant aboveground litter to soil organic carbon gradually decreased and the degradation rate of cutin gradually accelerated with the increase of soil depth.The contribution of root to soil organic carbon in 10-20 cm and 20-30 cm soil layer was significantly enhanced under the treatment of enclosure,and the contribution of root to 10-20 cm soil layer was significantly reduced under the treatment of mowing once a year.The content of cutin and suberin monomers was significantly positively correlated with the content of soil organic carbon.4)The treatment of enclosure and mowing once every two years promoted the accumulation of lignin in 0-10 cm soil layer,and the degradation rate of lignin was the slowest under the treatment of mowing once every two years.There was a significant correlation between the content of lignin and its phenolic monomers with the soil total organic carbon content.5)The content of soil total organic carbon,ligin and suberin was significantly positively correlated with the soil average temperature in growing season,soil total nitrogen content and underground biomass of the community,and the content of cutin in soil was significantly positively correlated with soil average temperature in growing season and total nitrogen content.