Mineralization Characteristics Of Soil Organic Carbon And Nitrogen,and Their Driving Factors Under Long-Term Different Fertilization Regimes In Fluvo-Aquic Soil

Soil bio-fertility plays an important role in maintaining soil fertility and farmland productivity.Based on the 39-year long-term fertilization experiment in Tianjin,six fertilization treatments were selected:no fertilization?CK?,chemical nitrogen fertilizer?N?,nitrogen,phosphorus and potassium fertilizer?NPK?,chemical nitrogen fertilizer+organic manure?NM?,chemical nitrogen fertilizer+green manure?NG?,chemical nitrogen fertilizer+straw?NS?.We determined the soil carbon and nitrogen sequestration and mineralization characteristics and soil microbiological characteristics.The main results are as follows:1)The application of balanced chemical fertilizer and organic materials significantly increased soil organic carbon and improved soil nutrient status.Soil pH were significantly reduced under N,NM and NS treatments?decreases by 0.42,0.35,0.42 units,respectively?.The application of organic manure significantly increased the available phosphorus content?increased 59 times?.Long-term different fertilization changed the distribution of soil aggregates.NPK,NM,NS and MG treatments significantly increased the quantity of 0.25-2 mm and<0.25 mm soil aggregates,and decreased the quantity of>2mm soil aggregate.But the mean weight diameter of soil aggregates significantly decreased under these treatments,which may due to Na⁺enrichment caused by long-term application of organic fertilizer destroyed the aggregate structure.NPK,NM,NS and MG treatments significantly increased the content of soil organic carbon,total nitrogen,total carbon and inorganic carbon in 0.25-2 mm soil aggregate.2)The application of organic materials significantly increased microbial biomass C and N.Long-term fertilization significantly shifted the microbial community structure and the activities of extracellular enzymes,NPK,NM,NS,NG significantly increased the abundance of all microbial groups and the geometric mean?GMea?of hydrolase activity.Soil community structure were mainly affected by soil organic matter and available phosphorus;and the main factors that driving the change of soil extracellular enzymes were soil total nitrogen and total phosphorus.Long-term fertilization changed the composition and abundance of bacterial and fungal communities.Chemical fertilizer decreased the abundance of Proteobacteria,whereas increased the abundance of Acidobacteria;the abundance of Chloroflexi decreased and the abundance of Firmicutes increased under NM treatment;Dothiomycetes abundance were decreased under NPK,NM,NS,NG treatments;while NPK and NM treatments increased the abundance of Pezizomycetes.3)The total explanation of soil chemical properties and bio-fertility to organic carbon and nitrogen mineralization was 75.37%.Organic carbon mineralization was significantly correlated with polyphenol oxidase,peroxidase,all PLFA groups,Proteobacteria,Acidobacteria and Chloroflexi bacteria.Microbial respiratory quotient?qCO₂?was positively correlated with Glomeromycota,Orbiliomycetes,Dothideomycetes.Organic nitrogen mineralization was positively correlated with BG;NAG;bacterial content and SMBC.In conclusion,different fertilization models mainly affect soil organic carbon and nitrogen mineralization by changing nutrient content to drive the shift of microbial community structure and extracellular enzymes in fluvo-aquic soil.The application of organic materials could increase soil nutrients,and followed by the increase of eutrophic bacteria;hydrolase activities;and the decrease of oxidase activities and oligotrophic bacteria,which to some extent decreased microbial respiration quotient,increased soil organic carbon turnover and organic nitrogen mineralization potential.