Long-term Fertilization Of Humus Group Carbon In Dryland Red Soil Aggregates And Its Relationship With The Structure And Function Of Microbial Communities

Upland red soils in southeast China usually possess a low fertility,especially with low levels of soil organic matter.Soil humus is an important component of soil organic matter,and has a regulating effect on soil fertility.Soil microorganisms directly participate in the formation of soil humus,and also act on the release of nutrients from soil humus.Therefore,soil humus is closely related to soil microorganisms,which has an important impact on soil organic matter and soil fertility.However,it is still unclear for the relationship between humus components and the composition and function of microbial community in soil aggregates,and the mechanism of humus components' influence on microbial community needs to be studied.This study selected five different long-term fertilization treatments: unfertilized control(CK),chemical fertilizer(NPK),double chemical fertilizer(2NPK),organic fertilizer(OM)and organic fertilizer combined with chemical fertilizer(OM + NPK)from Jinxian Red Soil Station in Jiangxi Province.Four sizes of soil aggregates were obtained(> 2000 ?m,250-2000 ?m,53-250 ?m,< 53 ?m)using wet sieve method.The humus components were extracted by “Humeomics” sequential extraction method,and the organic contents of humus components were analyzed.The composition and diversity of microbial community of soil aggregates were analyzed using Illumina Hiseq high-throughput sequencing.Besides,the activities of enzymes associated with the decomposition of organic matter were also determined.The carbon source-utilizing activities of soil aggregates were measured using Biolog eco microplate.By statistic analyses including correlation analysis,principal component analysis,and redundancy analysis,the effects of fertilization on the humeomics and the composition and diversity of microbial community of soil aggregates in upland red soil were studied,as well as the relationships between humeomics and microbial community of soil aggregates.The main results are as follows:(1)Long-term fertilization,especially for the organic fertilizer combined with chemical fertilizer treatment(OM + NPK),significantly increased the content of total organic carbon(TOC)and dissolved organic carbon(DOC)in soil and aggregates by 59.02% and 118.71%,respectively.For organic fertilizer treatments(OM,OM + NPK),the TOC content first increased then decreased with the decreasing aggregate size.For chemical fertilizer treatments(NPK,2NPK),the TOC content increased with the increasing aggregate size.Long-term organic fertilizer treatments(OM,OM + NPK)significantly increased the ratio of large aggregate,facilitating the aggregation of upland red soil.Long-term fertilization significantly increased the organic carbon content of each humus component,accounting for up to 48.3% of TOC of soil aggregates.The organic carbon content of humeomics among soil aggregates for a same fertilization treatment showed no significant difference.Two humus components,RESOM and ORG1,possessed the highest organic carbon contents among soil aggregates for each fertilization treatment.RESOM was the main influencing factor that significantly affected TOC of soil aggregates.(2)Long-term fertilization significantly changed the diversity and composition of bacterial and fungal communities of aggregates in upland red soil.Long-term double chemical fertilizer treatment(2NPK)significantly reduced the diversity of bacterial community of soil aggregates,whereas the organic fertilizer treatment(OM,OM + NPK)significantly reduced the diversity of fungal community of aggregates.For organic fertilizer treatments(OM,OM+NPK),the bacterial diversity of macroaggregates(> 250 ?m)was significantly higher than that of micro-aggregates(< 250 ?m),while the the diversity of fungal communities of aggregates was just the opposite.Long-term fertilization significantly altered the composition of bacterial and fungal communities.NPK and OM+NPK treatments significantly increased the relative abundances of Bacteroidetes and Firmicutes,and significantly decreased the relative abundance of Chloroflexi.2NPK and OM treatments significantly increased the relative abundances of Actinobacteria,and significantly decreased the relative abundance of Verrucomicrobia.Long-term organic fertilization treatments(OM,OM+NPK)significantly decreased the relative abundance of Ascomycota.Long-term chemical fertilization treatments(NPK,2NPK)significantly increased the relative abundances of Zygomycota.Both fertilization and aggregate size showed significant effects on the composition of bacterial and fungal communities of soil aggregates.The organic carbon content of soil humus component,RESOM,was the main influencing factor that significantly affected the bacterial community composition of soil aggregates,significantly and positively correlated with the relative abundance of Sphingomonas.ORG1 was the main influencing factor that significantly affected the fungal community composition of soil aggregates,significantly and positively correlated with the relative abundance of Acremonium.(3)Long-term fertilization,especially for the organic fertilizer combined with chemical fertilizer treatment(OM + NPK),significantly increased the activities of enzymes associated with the decomposition of organic matter in upland red soil aggregates,including sucrase,amylase,cellulase,?-glucosidase,?-glucosidase,?-xylosidase,and laccase.The organic carbon contents of four humus components,RESOM,ORG1,ORG2,and ORG3,were all significantly and positively correlated with the enzyme activities.Lone-term organic fertilization treatments(OM,OM+NPK)significantly increased the microbial carbon source-utilizing activity in upland red soil aggregates,while chemical fertilization showed no significant effect.The microbial utilizing activities of carbohydrates and amino acids were the main influencing factors that affected the bacterial community composition of soil aggregates,most significantly correlated with the relative abundance of Sphingomonas.The carbon source-utilizing diversity was the the main influencing factor that affected the fungal community composition of soil aggregates,most significantly correlated with the relative abundance of Acremonium.Significant correlation existed among RESOM,the relative abundance of Sphingomonas,and the utilizing activity of carbohydrates and amino acids,and among ORG1,the relative abundance of Acremonium,and AWCD.This study clarified the effects of long-term fertilization on humeomics and microbial community in upland red soil aggregates.The relationships between the organic carbon content of humeomics and the diversity and composition and the functional activity of aggregate microbial community were determined.Findings of this study would provide a fundamental basis for the application of organic fertilization to improve organic matter level in upland red soil.