The Source And Degradation Characteristics Of Plant Organicmatter In Soilof Main Steppe Community In Inner Mongolia

Understanding the stability mechanism of steppe soil organic matter is of great significance to the study of long-term carbon sequestration in steppe.In recent decades,ecologists have carried out extensive research on the stability mechanism of soil organic carbon reservoir in Inner Mongolia steppe,although the differences in carbon stocks have been recognized in different soil layers,there is a lack of in-depth understanding of the changes of plant carbon at the molecular level in soil organic matter in steppe ecosystem.This study took three main plant communities of desert steppe,typical steppe and meadow steppe as the research object,and the composition of free lipids and binding esters in 3 kinds of grassland plants were analyzed by chemical extraction and gas chromatography-mass spectrometry(GC-MS).The plant markers in the soil that can indicate the source of carbon from the leaves and roots were selected,based on which the contribution of plant leaves and roots to soil organic carbon formation was clarified,and the decomposition characteristics of plant carbon in soil were elucidated.The main conclusions were as follows:1.According to the biological molecular composition of plant leaves and roots as well as the soil,the biomarkers of plant carbon were divided into six categories: alcohol,alkane acid,?-hydroxyl acid,?,?-alkanedioic and medium and long chain substituted acid.In the steppe communities,n-alcohol(C16),n-alkane acid(C16:0,C18:0 and C18:3)and medium-length chain substituted acids(C18)were found to be specific biomarkers of the leaves,while long-chain alkane acid(C24,C26),?,?-alkanedioic(C16,C18),?-hydroxyl acid(C22 and C24)could be used as specific biomarkers of the roots.2.The vegetation communities root contributed more organic carbon to the soil organic carnon pool than leaves in the three steppe communities.3.The decomposition of plant leaves and roots of different steppe communities occurred to varying degrees after they entered into the soil,and the degradation degree of plant leaves is higher.