| Cadmium(Cd)pollution in paddy soils has always been a major problem in agricultural production and food security of China,affecting people’s health and social sustainable development,and has been widely concerned.Organic fertilizer is an important agricultural management measure,which plays an important role in providing soil nutrients,improving the quality of agricultural products and repairing soil pollution.Soil microorganisms are important parts of soils,which have an important indicative effect on soil health and play an important role in nutrient cycling as well as organic matter degradation,and is crucial to the growth and development of crops.Studying the effects of organic fertilizer application on soil microbial community diversity and structure,composition and network interaction and their dynamic changes in contaminated paddy fields has important guiding significance for agricultural fertilization management,remediation of Cd-contaminated paddy soils,soil health assessment,and crop growth and development.In this study,Cd-contaminated paddy soils in Huangshi City,Hubei Province was taken as the object,rhizosphere and bulk soils at different development stages such as tillering stage,heading stage,filling stage and mature stage were collected after applying organic fertilizer,and the dynamic changes of Cd content in soils and plants,bacterial and fungal communities were analyzed.1)Soil microbial community composition,network complexity and their dynamic changes.The main dominant bacteria phyla of paddy soils were Chloroflexi(22.87%),Proteobacteria(19.30%),Actinobacteriota(19.19%),Acidobacteriota(15.94%)and Myxococota(4.94%),accounting for 82.24% of the total bacteria.The dominant fungi classes were Sordariomycetes(56.06%),Dothideomycetes(11.74%),Tremellomycetes(5.02%)and Agaricomycetes(4.89%).Among them,the dominant classes(Sordariomycetes,Dothideomycetes)belonging to Ascomycota accounted for the largest proportion,67.80 %.From tillering stage to mature stage,the relative abundance of dominant bacteria Proteobacteria and Acidobacteriota increased gradually and then decreased slightly.The abundance of fungi Dothideomycetes showed an upward trend as a whole.The four network topology parameters,node number,degree,average path length and betweenness centralization showed a gradually increasing trend,which proved that the network complexity became more complicated with the extension of rice development stage.2)Effects of organic fertilizer application on soil microbial communities,available cadmium content in soils and cadmium absorption of rice.The application of organic fertilizer significantly decreased the α diversity of soil microbial communities,increased the abundance of dominant species in soils,and made the differences of community α diversity and structure,relative abundance of some dominant species(Myxococota,dothideomycetes and so on)larger among different development stages,however,it made the difference of network complexity smaller during each stage,especially between tillering stage and filling or mature stage.The effects of applying organic fertilizer on bacterial community diversity and structure,community composition were more obvious than those of fungi.Generally speaking,there was no obvious differences in community diversity,structure,composition and network complexity between rhizosphere soils and bulk soils.But the influences of environmental factors on rhizosphere soil bacterial communities were more significant than those of bulk soils,and fungi were just the opposite.In the soils with organic fertilizer application,the contents of available Cd in soils and Cd in rice grains decreased significantly and the decrease was the largest at mature stage,the contents of soil available Cd decreased by 42.1%(rhizosphere)and 33.4%(bulk),and the contents of grain Cd decreased by 73% at this stage.3)Key microorganisms and soil enzyme activities that affecting the content of available Cd in soils.The dominant Chloroflexi and Firmicutes of bacteria phylum level and Leotiomycetes of fungi class level,and the activities of 4-Methylumbelliferylβ-D-cellobioside and 4-Methylumbelliferyl β-D-xylopyranoside were positively correlated with the available Cd content in soil,while the dominant Proteobacteria and Myxococcota of bacteria phylum level and the activity of 4-Methylumbelliferyl N-acetyl-β-D-glucosaminide were negatively correlated with the available Cd content in soils.4)Environmental affect factors of soil microbial communities and available Cd content.Spearman correlation analysis showed that the diversity,structure,composition and network complexity of soil microbial communities in paddy soils were significantly affected by environmental factors,among which the most influential was the available Cd content of soils,followed by p H,organic carbon and ammonium nitrogen.Soil available Cd content was significantly affected by soil p H value and soil organic carbon,total carbon,total nitrogen,soil available phosphorus content.In summary,from tillering stage to mature stage in paddy soils,the difference of community structure became larger,the abundance of dominant species changed significantly,and the network complexity gradually increased.The application of organic fertilizer increased the relative abundance of dominant species at different growth stages,reduced αdiversity and network complexity,and significantly reduced soil available Cd and rice grain Cd content.The community diversity and structure,community composition and network complexity in rhizosphere and bulk soils were similar.This study revealed that the effects of organic fertilizer on the rhizosphere and bulk microbial communities in Cd-contaminated paddy soils and their dynamic changes during different growth stages,in addition,the key microorganisms and soil enzyme activities affecting the content of available Cd in soils were also revealed.These results provided important theoretical support for agricultural fertilization management,remediation of Cd-contaminated paddy soils,soil health assessment,and plant growth and development. |
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