Study On The Turnover Mechanism Of Soil Organic Carbon With Different Carbon Saturation Levels Under The Addition Of Exogenous Carbon

In order to explore the characteristics of soil organic carbon turnover at different carbon saturation levels,this study is based on two long-term positioning experiments with different carbon saturation levels in the northern dry-land(Zhengzhou,Henan)and the southern double-season rice paddy soil(Jianxican,Jiangxi).Single application of chemical fertilizer(NPK)and organic fertilizer(NPKM’)two carbon-saturated levels of soil,through indoor cultivation method,explore the different straw addition amount(0%,0.3%and 1%)soil aerobic(soil moisture content 75%)The characteristics of soil greenhouse gas emissions,aggregate distribution and aggregate organic carbon,activated carbon components and enzyme activity changes under flooded conditions.The main results are as follows:(1)In the 37-day indoor cultivation experiment,straw addition significantly increased the soil CO2 emission flux and cumulative emissions.The cumulative CO2 emissions of soils with high carbon saturation levels(2580.93～4184.43 mg/kg)were significantly higher than those with low carbon saturation levels.(918.15～2964.87 mg/kg).In the soil with the same carbon saturation level,the CO2 emission flux and cumulative emissions of high-stalk cultivation are greater than those of low-stalk cultivation.The CH4 emission flux and cumulative emission of the soils with different carbon saturation levels without straw and aerobic cultivation with straw are very low,which is negligible compared with the straw-immersed cultivation.A large amount of methane is produced in the flooded cultivation with straw added,which is expressed as a carbon "source." Under the same cultivation conditions,the methane emission flux and cumulative emission of soil with high carbon saturation level are significantly greater than that of low-carbon saturated soil.The cumulative methane emission is The soil with low carbon saturation level is 1.27～8.28 times.(2)Aerobic culture significantly increased the proportion of aggregate components of>0.25 mm and decreased the proportion of soil aggregates of<0.053 mm size.The early stage of submerged culture was not conducive to the formation of large aggregates.In the later stage of culture,the proportion of large aggregates Increased,GMD,MWD index increased,improved the stability of soil aggregates.The addition of straw increased the content of organic carbon in aggregates at each particle level,and the content of aggregate organic carbon in aggregates at each particle size was expressed as large agglomerates>micro-aggregates>sticky particles.Compared with before cultivation,large agglomerates The organic carbon content increased the most;the proportion of aggregated organic carbon in each culture treatment showed that the carbon of large aggregates increased significantly,and the percentage of sticky particles organic carbon decreased significantly,and it was the most significant under high straw cultivation.The proportion of organic carbon in large aggregates in soils with different carbon saturation levels was increased by 15.99%,9.52%,15.02%and 9.8%,respectively.(3)Compared with the control treatment,different carbon-saturated soils were significantly increased the activities of soil invertase,cellulase and β-glucosidase compared with the control treatment,but the increase range decreased with,the increase of carbon saturation level.In the same culture treatment,the activities of the three enzymes showed that the soil with high carbon saturation level was larger than that with low carbon saturation level.