Effect Of Caragana Tibetica Nebkhas Onsoil Organic Carbon In Shrub Desert Steppe

Carbon peaking and carbon neutrality have become hot issues in the international community.Shrub encroachment is common in arid and semi-arid steppe,but it is not clear whether the formation of nebkhas affects the distribution,source and stability of soil organic carbon in steppe ecosystems.This study took the Caragana tibetica nebkhas distributed in transition zone of the desert steppe and desert in Inner Mongolia as the research object.By investigating the characteristics of the plant community inside and outside the nebkhas and measuring the soil organic carbon content inside,outside and under the nebkhas during the different developmental stage,the effects of Caragana tibetica nebkhas on soil organic carbon content and its spatial distribution were clarified.Through analyzing the distribution characteristics of soil labile organic carbon,soil recalcitrant organic carbon and lignin,as well as the degradation degree of lignin inside,outside,and under the Caragana tibetica nebkhas in the stable stage,the influence of Caragana tibetica nebkhas on the source and stability of soil organic carbon was explored.The main results were as follows:(1)The formation of Caragana tibetica nebkhas significantly increased the soil organic carbon content inside the nebkhas,and the "fertility island effect" appeared.With the development of the nebkhas,the soil organic carbon content in the shallow layer(0-30 cm)and deep layer(30-100 cm)outside nebkhas,and that in shallow layer under nebkhas tended to increase,but the soil organic carbon content inside,outside and under the nebkhas did not change significantly.(2)In the stable stage of Caragana tibetica nebkhas,the content of soil lignin and its monomers inside,outside and under the nebkhas decreased gradually with the increase of soil depth,while the lignin content inside the nebkhas was significantly higher than that under and outside the nebkhas indicating that the formation of the nebkhas promoted the input of plant derived organic carbon inside the nebkhas.(3)In the stable stage of Caragana tibetica nebkhas,the content of labile and recalcitrant organic carbon inside,outside and under the nebkhas decreased and the recalcitrance carbon indices increased gradually with the increase of soil depth.Compared with those outside and under the nebkhas,the content of soil recalcitrant carbon and the degree of lignin degradation increased significantly and the recalcitrance carbon indices inside the nebkhas decreased,indicating that the formation of nebkhas reduced the stability of soil organic carbon inside the nebkhas,but with the input of plant derived organic carbon the degradation of plant derived organic carbon slowed down.The formation of the nebkhas made the impact of shrubs on the content,spatial distribution,formation and stability of steppe soil organic carbon more complicated and was of more uncertainties.The results of this study can provide basic data and theoretical support for the rational utilization and protection of shrub encroachment steppe,and also provide a scientific basis for accurately assessing the stability of the soil carbon pool in shrub encroachment steppe.