Characteristics And Mechanisms Of Organic Matter Mineralization Influenced By Fertilization And Land Use In Red Soil And Paddy Soil

In the terrestrial ecosystem,soil organic matter is a crucial carbon pool.The mineralization of soil organic matter is tightly related to soil fertility and climate change.Fertilization and land use are the important management practices of the soil.The effects of fertilization and land use on the mineralization of soil organic matter are of great research significance.In this study,red soil and paddy soil were investigated to explore the effects of long-term fertilization and the land use on the mineralization of soil organic matter and the underlying mechanisms.The main contents includes that(1)the incubation experiments and the mineralization dynamic models were used to describe the characteristics of soil organic matter mineralization;(2)the fluorescence spectroscopy,the nuclear magnetic resonance spectroscopy,and the thermal pyrolysis-gas chromatography/mass spectrometry were applied to analyze the chemical composition of soil organic matter;(3)the high-throughput sequencing and the enzyme activity measurement were carried out to explore the roles of microbial community and function in the decomposition of soil organic matter;(4)the physical separation,chemical extraction and X-ray diffraction technology were conducted to investigate the regulations of aggregate size and mineral composition on the mineralization of soil organic matter.(5)the statistical analyses were employed to explore the relationships between the chemical composition of organic matter,the microbial community and hydrolase activity,the mineral composition and the aggregate size,and their roles in the mineralization of soil organic matter.The main results are summarized as follows:(1)The rate and amounts of organic matter mineralization were facilitated by the long-term applications of chemical and organic fertilizers in the red soil.The sequence of control<chemical fertilizer<chemical fertilizer+straw<manure was observed in the contents of total organic carbon,organic carbon pool,dissolved organic carbon and microbial biomass carbon of red soil among the fertilizations.The proportion of organic carbon associated with Fe/Al oxides in the total organic carbon revealed an opposite trend among the fertilizations.The chemical and organic fertilizations increased the relative abundance of Actinobacteria,Proteobacteria and Ascomycota,as well as the activities of?-glucosidase and invertase.Structural equation modeling suggested that the activities of organic carbon hydrolases,the labile organic carbon,the composition and diversity of microbial community were positive factors in governing the organic matter mineralization of the red soil.Among these factors,the activities of carbon hydrolases played the dominant roles,and the labile organic carbon was more important than the composition and diversity of microbial community.These results demonstrated that the promotions of fertilizations on the mineralization of organic matter were largely drove by the increased activities of organic carbon hydrolases in the red soil.(2)The amounts of organic matter mineralization were increased with the decreasing size of the aggregate in the red soil.The high concentrations of dissolved organic matter were found in the small size of aggregates,while the chemical structure of dissolved organic matter showed the opposite tendency.The activity of?-glucosidase in the aggregates increased as the aggregate size decreased,and the the abundances and diversities of GH1?-glucosidase microorganisms followed the similar trend.The microorganisms harboring GH1?-glucosidase genes in the aggregates mainly included Actinobacteria,Alphaproteobacteria,Gammaproteobacteria,Flavobacteria,Eurotiomycetes and Sordariomycetes.The relative abundances of Actinobacteria,Sordariomycetes,and Eurotiomycetes were significantly different among the aggregate sizes.Redundancy analyses suggested that the dissolved organic matter and the pH were critical factors in influencing the GH1?-glucosidase microorganisms at the aggregate scale.Structural equation modeling revealed that the regulation of aggregate size on the mineralization of organic matter was mostly controlled by the activity of?-glucosidase and the dissolved organic matter in the red soil.(3)The rate and amounts of organic matter mineralization in organo-mineral complexes were markedly stimulated by the fertilizations in the red soil,especially the organic fertilizations.The type and diversity of organic matter composition in organo-mineral complexes was strikingly increased by the applications of chemical and organic fertilizers.The abundances and diversities of GH1?-glucosidase microorganisms and the activity of?-glucosidase in organo-mineral complexes showed no clear difference among the fertilizations.The fertilizations observably changed the community composition of GH1?-glucosidase bacteria,but had no significant effect on the community composition of GH1?-glucosidase fungi in organo-mineral complexes.The dominant microorganisms harboring GH1?-glucosidase genes in organo-mineral complexes were Actinobacteria,Betaproteobacteria,Deltaproteobacteria,Gammaproteob,Rubrobacteria,Eurotiomycetes and Sordariomycetes.The contents of Fe/Al oxides and associated organic carbon in organo-mineral complexes revealed clearly different among the fertilizations.The organic carbon attributes played the important roles in the mineralization of organic matter in organo-mineral complexes of the red soil.(4)The mineralization of organic matter was inhibited by the applications of chemical fertilizers,while the suppression was alleviated or reversed by the partial substitution of chemical fertilizers with green manure in the paddy soil.The contents of organic carbon were increased by all examined fertilizations,and the proportion of labile organic carbon in total organic carbon showed the similar pattern to the mineralization.The fertilizations weakly influenced the abundance and the diversity of microorganisms,but strikingly shifted the composition of the microbial community in the paddy soil.The dominant microorganisms included Proteobacteria,Acidobacteria,Actinobacteria,Chloroflexi,Firmicutes,Mortierellomycota and Ascomycota in the paddy soil.The bacterial community composition was strongly linked with the NO₃^--N and the pH,and the fungal community composition was tightly connected with the organic carbon components in the paddy soil.The partial substitution of chemical fertilizers with green manure markedly increased the activities of organic carbon hydrolases,but generally had no significant effect on the abundance of genes encoding these hydrolases in the paddy soil.The activities of?-glucosidase and cellobiohydrolase were mainly affected by the total organic carbon in the paddy soil.Random forest analysis and Partial least squares path modeling indicated that the partial substitution of chemical fertilizers with green manure regulated the mineralization of organic matter largely by modulating the organic carbon components in the paddy soil.(5)The mineralization of organic matter was strikingly changed by the land use in the red soil,and followed the sequence bamboo plantation<camphor plantation<tea plantation.The higher carbon contents of labile and recalcitrant pools were in the camphor plantation and the tea plantation than that in the bamboo plantation.The content of dissolved organic matter revealed the order bamboo plantation<camphor plantation<tea plantation,while the complexity of chemical structure in the dissolved organic matter followed the opposite trend.The land use markedly shifted the bacterial and the fungal community structure,and the relative abundances of Actinobacteria,Acidobacteria,Firmicutes and Basidiomycota in the red soil.The multivariate regression tree results indicated that the total organic carbon and/or the C/N ratio were dominant factors in influencing the bacterial and fungal communities.Moreover,the redundancy analysis results demonstrated that the communities of bacteria and fungi in bamboo plantation,camphor plantation and tea plantation were tightly linked to the C/N,the pH and labile carbon pool I,and the dissolved organic matter,respectively.Pearson's correlation results revealed that the mineralization of organic matter was strongly correlated with the organic carbon components,but generally not the microbial community composition,which speculated that the organic carbon components were the major determinant in controlling the organic matter mineralization under the land use.In this tudy,the roles of organic matter component,microbial community and function,enzyme activity,and mineral composition in the mineralization of organic matter was systematically explored at the scales of bulk soil,aggregates and organo-mineral complexes in red soil and paddy soil under the fertilization and the land use.The study provided a scientific basis for understanding the carbon cycle of subtropical terrestrial ecosystem and climate change.