Effects Of Enclosure On Vegetation-soil Features Of The Leymus Chinensis Grassland: Emphasizing The Changes In Soil Organic Carbon Fractions

To increase the carbon stock in the terrestrial ecosystem is one of key measures in mitigating climate change,and much efforts have been put on the study of the mechanisms underlying the soil organic carbon(SOC)dynamics.Soil organic carbon fractions are important indicators for evaluation of SOC dynamics,and have become a research hotspot in recent studies in soil science,environmental science and ecological science.Grazing exclusion by fence is one of the main measures for restoring degraded grasslands.It is essential to study the dynamic features of grassland vegetation and soil under long-term grazing exclusion,especially the changes of SOC fractions,for understanding the interactive mechanisms of plant and soil factors under long-term grazing exclusion,and to provide a theoretical basis for developing new ideas and formulating strategies for the restoration of degraded grassland.We studied the effects of long-term grazing exclusion on vegetation and soil conditions,especially SOC fractions,in a temperate,semi-arid grassland dominated by Leymus chinensis in central Inner Mongolia.These involved the studies at two enclosure experiments.The enclosure experiment in sample plot A started in 1979 and 1999,and the enclosure experiment in sample plot B started in 1983.The SOC fractions,and other soil and vegetation attributes were investigated in summer 2019 in the no-grazing enclosure and on the free-grazing grassland,and comparatively analyzed.Our results showed that1.Long-term enclosure increased plant community above-gound biomass,cover,height,species diversity and richness of the L.chinensis grassland.Long-term enclosure increased the content of soil clay,silt,free iron and aluminium oxidation and cation exchange capacity(CEC).Clay,silt,free state oxides and CEC had a significant effect on SOC fractions(P<0.05).2.Long-term enclosure increased the total SOC content,particulate organic carbon(POC)and microbial mass carbon(MBC)in the L.chinensis grassland.It increased the proportion of POC,but decreased that of MAOC,MBC,or DOC,in total SOC.3.POC showed a highly significant and positive correlation with rootstock carbon(P<0.001),MAOC showed a highly significant positive correlation with soil water content and DOC,MBC showed a significant positive correlation with aboveground and belowground biomass,and DOC showed a significant positive correlation with soil water content.4.The content of SOC,POC,MBC,DOC,as well as the proportion of POC,MBC,DOC in SOC and cation exchange capacity,can be used as indicators for grassland recovery.The proportion of MAOC in SOC can be used as an indicator for grassland degradation.