Effects Of Precipitation Variation On Soilorganic Catbon Dynamics In Stipa Breviflora Shrub Desert Steppe

Precipitation variation is an important part of global climate change.The desert steppe is sensitive to the change of precipitation and the phenomenon of shrub encroachment is common.The formation and stabilization mechanism of soil organic carbon in desert steppe is still unclear due to the complexity of input and output of soil carbon under the combined influence of precipitation change and shrub encroachment.This study took Stipa breviflora shrub desert steppe as the research object,and established an experimental platform to simulate rainfall changes(precipitation decreased by 30%,natural precipitation,precipitation increased by30%,and precipitation increased by 50%).By analyzing the biomolecular composition of different tissues of dominant plants and that of soil organic carbon in Stipa breviflora community under different precipitation treatments,we screened out the biomarkers indicating the input of aboveground and underground organic carbon by plants,and clarified the main sources of plant derived organic carbon in shallow soil under different precipitation treatments.By analyzing the distribution characteristics of soil labile organic carbon,recalcitrant organic carbon and total organic carbon and the degradation degree of plant derived organic carbon in soil under different precipitation treatments,the stability of soil organic carbon in shallow layer was explored,and the effects of precipitation on the formation and stability of soil organic carbon in Stipa breviflora shrub desert steppe were systematically studied.The results can provide a theoretical basis for predicting the potential of soil carbon sequestration in the shrub desert steppe under the background of rainfall change,and also provide a reference for the development of management measures for increasing soil organic carbon sink.The main results were as follows:(1)The plant species composition and plant importat value in Stipa breviflora shrub steppe changed obviously under different precipitation treatments.With the increase of precipitation,the species number of perennial forbs increased gradually,and the important values of Artemisia frigida,Leymus chinensis and Artemisia scoparia increased,while the species number and important values of perennial tupitgrasses decreased gradually,and the important values of Chenopodium aristatum decreased,especially in the shrub patches.(2)The decrease of precipitation significantly reduced the SOC content in the0-10 cm soil layer of herbaceous matrix and the shrub nebkhas,but there was no significant difference in SOC content between the shrub patch and the herbaceous matrix.The content of soil recalcitrant organic carbon was significantly increased under the precipitation plus 50%.The content of soil recalcitrant organic carbon in shrub patch under natural precipitation was significantly higher than that in 0-10 cm soil layer of herbaceous matrix,while the content of soil recalcitrant organic carbon in shrub patch under reduced or increased precipitation was significantly lower than that in 0-10 cm soil layer of herbaceous matrix.(3)Under different precipitation treatments,the soil organic carbon in the shrub nebkhas,the herbaceous matrix and the 0-10 cm soil layer under the shrub nebkhas mainly came from the leaves,stems and roots of plants.And the soil organic carbon in the 10-20 cm soil layer of herbaceous matrix and under shrub nebkhas mainly came from the roots of plants.However,the contribution degree of Suberin,Cutin and lignin to soil organic carbon of herbaceous matrix and shrub patch was different under different precipitation treatments.(4)There was no significant difference in soil recalcitrant carbon index between herbaceous matrix and the shrub patch,indicating that the change of precipitation did not change the stability of soil organic carbon of shallow layer in the shrub steppe of Stipa breviflora.However,the increase of precipitation changed the decomposition dynamics of plant derived soil organic carbon in the 10-20 cm soil layer under the shrub nebkhas,in which the degradation of lipids was accelerated and that of lignin was slower.Under the condition of natural precipitation,the recalcitrant carbon index of shrub patch was significantly higher than that of herbaceous matrix,while under the treatments of precipitation plus 50%,the recalcitrant carbon index of shrub patch was significantly lower than that of 0-10 cm soil layer of herbaceous matrix.These results indicated that the increase of precipitation decreased the stability of soil organic carbon in shrub patches,which may be related to the input of unstable plantderived organic carbon from Caragana microphylla.