Changes Of Soil Organic Carbon Components And Relationships With Soil Microbial Diversity In Wheat-Maize Crop System

Soil carbon sequestration is very important for improving soil quality and alleviating climate changing.Different tillage methods and straw returning have significant influence on soil organic carbon components.However,the dominant mechanism of soil carbon sequestration is not clear.The study on soil carbon sequestration from the perspective of microorganism will better explain micro ecological mechanism of soil carbon sequestration,which is of great guiding significance for improving soil carbon sequestration ability and increasing crop yield.This experiment is based on the winter wheat and summer maize ecosystem in the North China Plain,based on fourteen year long-term conservation tillage and straw returning farmland?beginning in 2002?.The effects of full straw returning?F?and no straw returning?0?under conventional tillage?C?,subsoil tillage?S?and rotary tillage?R?on soil basic physicochemical properties,soil organic carbon components,microbial communities and crop yield were studied,and the influencing factor in crop yield and soil organic carbon components was also explored.The main results were as follows:1 Effects of tillage and straw returning on soil organic carbon componentsStraw returning significantly increased the SOC content in two soil layers.The SOC content was the highest under subsoil tillage in 0-15 cm soil layer and the highest under conventional tillage in 15-30 cm soil layer.Straw returning significantly increased microbial biomass carbon content at jointing stage and filling stage of wheat and maize,but significantly reduced the microbial biomass carbon content at harvest stage.Soil microbial biomass carbon content in the 0-15 cm soil layer showed that subsoil tillage was significantly higher than that of conventional tillage and rotary tillage 58.3%and 22.2%.While in the 15-30 cm soil layer,the conventional tillage was the highest,significantly higher than that of subsoil tillage and rotary tillage 6.9%and 29.6%,and the subsoil tillage was significantly higher than that of the rotary tillage 21.2%.In the 0-15 cm soil layer,the soil dissolved organic carbon content was significantly increased under straw returning,and was significantly under subsoil tillage higher than that of conventional tillage and rotary tillage 7.3%and 7.9%.But in the 15-30 cm soil layer,the conventional tillage was significantly higher than that of the subsoil and rotary tillage 7.5%and 17.9%,and the subsoil tillage was significantly higher than that of the rotary tillage 12.6%.2 Influencing factor of soil organic carbon componentsCompared with no straw returning,straw returning only significantly increased the soil water content in 0-15 cm soil layer.Compared with the conventional tillage,the average soil water content under subsoil and rotary tillage significantly increased by 11.8%and 6.7%,respectively.Soil bulk density decreased from wheat jointing stage to wheat harvest stage,but increased from maize jointing stage to maize harvest stage.Straw returning only significantly reduced the soil bulk density in 0-15 cm soil layer.Compared with conventional tillage,the bulk density under subsoil tillage was the lowest,and the soil bulk density was significantly reduced by subsoil and rotary tillage in two soil layers.The soil pH value in the 0-15 cm soil layer was acidic.Compared with the no straw returning,straw returning significantly increased only 1.7%of the soil layer pH value in the 0-15 cm soil layer,and the average pH value was 7.10 under the subsoil tillage in the 15-30 cm soil layer,which was significantly higher than conventional tillage and rotary tillage 14.7%and 9.4%.The average soil total nitrogen content under straw returning was 15.6%higher than that of no straw returning,and the total nitrogen content under the conventional tillage was lowest in 0-15 cm soil layer,which was significantly lower than that of subsoil tillage and rotary tillage,while the conventional tillage was significantly higher than that of subsoil tillage and rotary tillage in 15-30 cm soil layer.The total organic carbon was mainly influenced by total nitrogen,bulk density and water content.Microbial biomass carbon was mainly influenced by total nitrogen and water content,and soluble organic carbon was mainly affected by total nitrogen.Soil water content,bulk density,total nitrogen and pH significantly affected the function and structure of soil microbial community.High soil bulk density had negative effects on carbon metabolic ability and function of soil microbial community in C0 and R0treatment,while higher soil water content and total nitrogen content and the suitable pH value significantly increased the metabolic capacity and diversity of the microbial carbon source in the SF treatment,and also promoted the evolution of the microbial community structure in the SF treatment to the accumulation of organic carbon components.Soil microbial community significantly affected soil organic carbon components.The total organic carbon,microbial biomass carbon and dissolved organic carbon were positively correlated with the metabolic intensity of soil microbial carbon source.The abundance of soil microbial species can predict the changes of soil organic carbon fractions to some extent.The soil organic carbon was mainly affected by the Proteobacteria and the Verrucomicrobia,and the microbial biomass carbon was mainly affected by the Proteobacteria,and the dissolved organic carbon was mainly affected by the Firmacutes.Functional abundance of microbial genes can also predict changes in the contents of organic carbon components.The soil organic carbon had a significant positive correlation with the metabolic pathway of CO₂ fixation associated with carbohydrate metabolism in the SEED database.Soil microbial biomass carbon was significantly positively correlated with the metabolic pathway of carbohydrate?L2?,central carbohydrate metabolism,and one-carbon Metabolism.Soil dissolved organic carbon was significantly positively correlated with the metabolic pathway of central carbohydrate metabolism,monosaccharides and one-carbon metabolism.3 Influencing factor of crop yieldSubsoiling and straw returning significantly increased the yield of wheat and maize.With soil organic carbon?x₁?,microbial biomass carbon?x₂?and dissolved organic carbon?x₃?as independent variables,wheat yield?y₁?and maize yield?y₂?were selected as the dependent variables,and the stepwise linear regression analysis was carried out.The regression equation was as followsy1?28?.04 96x1?10?0.433x2?r?28?0.86,p?27?0.01?y2?28?-10.3 9x2?10?11.167x3-0.088?r?28?0.999,p?27?0.01?Wheat yield was mainly affected by soil organic carbon and microbial biomass carbon.Maize yield was mainly affected by microbial biomass carbon and dissolved organic carbon.Therefore,SF treatment is the best combination mode to improve soil carbon sequestration and microbial diversity.Subsoil tillage and straw returning both significantly improve soil physical and chemical properties,which can lead to the variation of function and structure of microbial community,and then influence the change of soil organic carbon components,and eventually significantly increased the crop yield.