Characteristics And Mechanism Of Soil Carbon Transformation Under Water And Fertilizer

Soil organic carbon pool and inorganic carbon pool were important components of soil carbon pool.The conversion of soil carbon and its exchange with the atmosphere will have a profound impact on soil quality and the concentration of greenhouse gases in the atmosphere.At present,there have been many studies on the total soil carbon pool or active organic carbon pool,but relatively few studies have been conducted on the change characteristics of soil inorganic carbon and its components.Changes in water and fertilizer conditions will significantly effect the changes in soil carbon pool,which is closely related to the participation of soil enzymes and microorganisms.The newly reclaimed soil in the coal mining subsidence area has the characteristics of poor structure and low nutrient content.The study of the carbon change of the reclaimed soil underwater and fertilizer treatment have certain guiding significance for the carbon fixation of the reclaimed soil and the improvement of soil quality in the mining area.Therefore,in this study,the newly reclaimed soil in the coal mining subsidence area of Liuxin Mine in Xuzhou was used as the test soil,and the indoor cultivation experiment was carried out.Study the characteristics of soil carbon pool changes under the action of water and fertilizer,differences in soil enzyme activity and microbial community structure characteristics under different water and fertilizer treatments,and the link mechanism between soil microbes and carbon transformation.The main findings are as follows:（1）The increase in soil moisture content and fertilization can both promote CO₂emissions.The CO₂ emissions of nitrogen fertilizer combined with organic fertilizer（W+N+O）treatment under the same moisture are higher than that of only nitrogen fertilizer（W+N）treatment.The effects of water and fertilization treatments on the concentration of CH₄ emissions are relatively small.After water and fertilizer treatment and cultivation,the total organic carbon content of the soil increased,and the total inorganic carbon content decreased.Under CK treatment,with the increase of water content,the change of total organic carbon decreased,and the change of total inorganic carbon increased.The soil SOC of different fertilization treatments is roughly expressed as W+N+O>CK>W+N.After water and fertilizer treatment,the inorganic carbon content of the soil is significantly reduced,and fertilization will further promote the decomposition of inorganic carbon.（2）The carbon distribution status of each component of the tested soil is MIC>MOC>PIC>POC>DIC>DOC.MOC,DOC,PIC,and MIC are all affected by fertilization and the interaction of water and fertilizer.Water has a greater impact on MIC and DIC in the inorganic carbon components.The contents of POC,DOC,and PIC all increased to a certain extent after cultivation.With the increase of water content,the release of DOC and DIC increase,and the effect of W+N+O treatment on soluble carbon is better than that of W+N treatment.The POC and PIC of the fertilization treatment under W3moisture were lower than those of the no fertilization treatment.Under the fertilization treatment,the difference in MOC content between different waters was small.Nitrogen fertilizer alone was not conducive to MOC accumulation,and the W3NO treatment had the highest MOC content.The MIC content of the soil was significantly reduced after cultivation.The MIC content and the distribution ratio of soil carbon in the fertilization treatment were the lowest in W1 water,indicating that fertilization under low water conditions promotes MIC decomposition.Unstable carbon（particulate carbon,soluble carbon）has a higher content and proportion under W1 moisture,and lower under W3moisture.The change of stable carbon（mineral-bound carbon）is the opposite.（3）Both water and fertilizer treatments can promote the increase of soil enzyme activity,and the effect of fertilization is better under suitable water conditions.With the increase of water content,the activities of invertase,urease,and phosphatase all increase,and fertilization treatment further promotes the increase of the activities of these three enzymes.Catalase activity increased to a lesser degree with water,and the fertilization treatment was lower than that of CK catalase activity.The soil invertase activity under W1 and W3 water treatments with W+N+O were significantly increased,and the invertase activity of the same water was W+N+O>W+N>CK.The activities of urease,catalase,and phosphatase showed that the W+N treatment was higher than the W+N+O treatment,and the activity was higher under the water condition of W2.Removing the original organic carbon content of the soil will significantly reduce the activities of invertase,urease and catalase.（4）In general,water shortage significantly reduces PLFAs,W+N+O treatment will increase the total amount of soil PLFAs,and W+N treatment will slightly decrease.The effects of water and fertilization treatments on dominant flora such as G+,G-,fungi,and actinomycetes all reached a significant level,and the interaction of water and fertilizer had no significant effect.The content of G-and G+showed that W+N+O was higher than that of W+N treatment,while the content of fungus was the opposite.Only applying nitrogen fertilizer will inhibit the activity of anaerobic bacteria,actinomycetes,and general bacteria.With the increase of water content,the ratio of G+/G-decreased,and the ratio of fungi/bacteria increased.Compared with W+N+O treatment,W+N treatment has higher relative abundance of Gram-negative bacteria and fungi.The physiological stress intensity of low-water microorganisms is greater,and the physiological stress intensity of W+N treatment is greater than that of W+N+O.The microbial community structure under W2moisture is the most stable,and the microbial community structure of W+N+O is more stable than W+N.The soil microbial community structure differs greatly under different water and fertilizer environments,and the community structure of the W+N treatment differs greatly under different water conditions.Under the same water conditions,the community structure of W+N+O treatment and no fertilization treatment is similar,but it is quite different from W+N treatment.W+N+O treatment is more closely related to general bacteria,G+,actinomycetes and eukaryotic bacteria.（5）Soil organic carbon and inorganic carbon undergo mutual transformation under different water and fertilizer conditions,and MIC,DOC,POC and CO₂ make major contributions to the carbon transformation process.Soil enzymes and microorganisms participate in the process of soil carbon conversion.The active components（DOC,POC）of the soil organic carbon components are easily used by aerobic bacteria,invertases,and actinomycetes.They emit CO₂ through respiration or promote the mineralization of organic carbon.MOC is indirectly affected by catalase and decomposes slowly.In different water environments,microorganisms participate in the conversion between CO₂ and CH₄.The p H and CO₂ partial pressure in the culture flask will affect the dissolution and precipitation of inorganic carbon.Urease,G-,phosphatase,and fungi can promote the decomposition of carbonate.The difference in the structure of the microbial community will affect the difference in the use of carbon sources.The W2NO and W3NO treatments have similar microbial community structures and similar carbon sources.Sucrase,actinomycetes,general bacteria,and fungi promote the accumulation of organic carbon in a stable form through turnover in the body or combination with minerals.