Study On Soil Organic Carbon And Microbial Characteristics Of Reclaimed Coal Mining Subsidence Area Under Long-term Fertilization

Soil organic carbon is an important index of soil fertility and the core of soil quality and function.Organic carbon is composed of various carbon fractions with different essential characteristics.The structure,decomposition rate and activity of different carbon fractions are different,and the response of different carbon fractions to soil management measures is also very different.Soil microorganism is an important factor influencing and controlling soil organic carbon transformation.Due to the large area of coal mining in Shanxi Province,the land,especially the farmland,collapsed seriously.The prominent problems existing in reclaimed soil are low organic carbon content and poor microbial activity.The improvement of organic carbon is the difficulty and key to the improvement of reclaimed soil quality.Therefore,based on the long-term location test of the mining subsidence reclamation area in southeastern Shanxi Province,this paper studied the changes in the quantity and structure of soil organic carbon and carbon fractions in reclaimed farmland under long-term fertilization.The response of soil microbial community and metabolic characteristics to fertilization during reclamation was studied.The relationship between soil microorganism and carbon turnover was analyzed.The results are of great scientific significance for understanding the composition,structure and microbiological characteristics of organic carbon in reclaimed soil under different fertilization measures and enriching the theoretical basis of soil quality recovery in reclaimed farmland.The main findings are as follows:(1)Fertilization measures rather than reclamation methods are the main factors affecting the recovery of organic carbon in reclaimed soil.h NPKM treatment is the best fertilization measure to promote the recovery of organic carbon in reclaimed soil.After 10 years of reclamation,the soil carbon sequestration speed was the highest in h NPKM treatment,and the CMI of h NPKM treatment was significantly higher than that of normal farmland(NL).Among the organic carbon fractions in soil,the sensitivity of ROC to fertilization was the highest.(2)The chemical structure of soil total organic carbon(SOC)under each fertilization treatment was mainly alkoxy carbon,which was shown as alkoxy carbon > alkyl carbon > aromatic carbon > carbonyl carbon.Soil organic carbon treated with h NPKM showed a higher degree of humification,and the organic carbon structure of clay binding was more stable than that of coarse sand and fine sand.After 10 years of reclamation,the proportion of alkoxy carbon in the soil treated with chemical fertilizers increased,while the proportion of carbonyl carbon decreased.The combination of organic and inorganic fertilizers increased the proportion of alkyl carbon and carbonyl carbon,reduced the proportion of alkoxy carbon and aromatic carbon,and increased the value of alkyl C/ alkoxy C(A/OA).As the particles become finer(from coarse sand,fine sand to clay),the proportion of alkoxy carbon and aromatic carbon decreased,while the ratio of alkyl carbon and carbonyl carbon increased,and the value of A/OA increased.(3)The geometric mean of the assayed enzyme activities(GMea)of reclaimed soil showed: NL=h NPKM>NPK>CK.In the process of soil microbial metabolism with h NPKM treatment,the restriction degree of energy relative to nutrient was higher than that of NPK and CK,and lower than that of NL.However,in the process of soil microbial metabolism with h NPKM treatment,the limitation of phosphorus to nitrogen was significantly higher than that of NPK,CK and NL.The activity of carbon enzyme,phosphatase and nitrogen enzyme was significantly lower than that of NL.The activity of soil carbon enzyme and phosphatase under different fertilization showed h NPKM>NPK>CK,and that of soil nitrogen enzyme showed NPK>h NPKM>CK.Compared with CK,the C/N ratio of extracellular enzyme activity in soil with NPK and h NPKM increased by 26.93% and 55.80%,while the C/P ratio increased by 31.20% and 42.62%,respectively.(4)Long-term fertilization increased the Shannon index of soil microorganisms,and h NPKM significantly increased the Mc Intosh and Simpson index of microbial community,but they were all lower than NL,showing NL > h NPKM > NPK > CK.Compared with CK,NPK significantly increased the utilization of carbohydrates and polymers by microorganisms by 50% and 36%,and significantly reduced the utilization of amines and lipids by 48% and 32%,respectively.h NPKM significantly increased the utilization of sugars and lipids by 31% and 49%,respectively,and significantly reduced the utilization of amines,polymers and amino acids.Microbial metabolic diversity of reclaimed soil was significantly correlated with soil enzyme activity and physicochemical properties.(5)Long-term fertilization increased the quantity and diversity of bacteria and fungi in reclaimed soil and changed the network structure of microbial community.The changes of organic matter,total nitrogen and p H were the main factors that affected the structure differences of bacteria and fungi.h NPKM showed the greatest improvement in bacterial and fungal diversity.Compared with CK,the connections in the ecosystem of bacteria and fungi with long-term application were denser,and the dispersion was reduced.More ecologically similar functional groups were formed in the microbial network with h NPKM,and the modularity was declined.The relationship was more competition than collaboration among microorganisms for soil nutrients in h NPKM and NL treatment.Fungi recovered faster than bacteria.(6)The total organic carbon and carbon fractions of reclaimed soil were significantly correlated with extracellular enzyme activity,microbial diversity and community.