Effects Of Fertilization Imbalance On Bacterial Community Composition And Diversity In Vegetable Corn

Vegetable corn is one of the most significant vegetables in China,which includes high protein,rich soluble sugar and vitamin.As the largest planting area and the largest total production amount of vegetable corn in the world,the vegetable corn is still the vegetable with the larger demand gap.Agricultural management based on chemical fertilization is the main way to regulate soil fertility and increase the yield of vegetable corn.However,fertilization not only increases the yield of vegetable corn,but also causes problems such as soil compaction in farmland,which has a great impact on the nutrient balance in farmland.Bacteria can decompose organic matter and promote the absorption of plant nutrients,which plays an important role in farmland systems.However,there is still a lack of comprehensive understanding of how bacterial communities in the plant-soil continuum respond to nutrient imbalance at different vegetable-maize growth stages.Based on the fertilization control experiment in corn field,this study set up 5 experimental treatments: including no fertilization(CK),nitrogen deficiency fertilization(PK),phosphorus deficiency fertilization(NK),and potassium deficiency fertilization(NP),nitrogen,phosphorus and potassium fertilization(NPK).Leaf,root,rhizosphere soil and soil samples of vegetable maize were collected at the jointing,booting,filling and maturity stages of maize growth.The composition and diversity of vegetable maize bacteria and the response of bacterial network structure to nutrient imbalance were studied by culture and non-culture methods.In total,6464 strains of root and rhizosphere soil bacteria were isolated and cultured for vegetable maize,among which 4862 strains were nitrogen fixing,phosphorus solving and potassium solving bacteria.The dominant groups were genus Pseudomonas,Bacillus,Stenotrophomonas,and Ensifer.These bacteria groups have been proved to be the key groups involved in nutrient cycling.A total of 4669 bacterial manipulation taxa(OTUs)were obtained from 320 samples by ribosomal small subunit(16S)amplicon sequencing.Substitution multivariate analysis of variance showed that fertilization treatment,growth stage and ecological niche all significantly affected the bacterial community composition of maize.The nutrient imbalance can recruit nutrient-efficient microorganisms,and the dominant groups are Actinomyces,Planctomyces,Proteobacteria,Bacteroidetes and Gemmatimonadetes.The bacterial community composition of vegetable maize was significantly affected by P fertilizer and K fertilizer.The bacterial community composition of vegetable maize showed obvious difference at different growth stages.Due to host plant specificity,the relative abundance of bacteria in vegetable maize was significantly different among different compartents.Analysis of variance found that fertilization treatment and ecological niche had significant effects on bacterial diversity of vegetable maize.The bacterial community diversity of rhizosphere soil and non-rhizosphere soil was significantly greater than that of leaf and root bacterial community.Under nutrient imbalance,the bacterial networks in different ecological niches of vegetable maize had scale-free characteristics and small-world characteristics,indicating that the bacterial networks in vegetable maize were non-random.Under nutrient imbalance,different ecological niches of vegetable maize recruited specific bacterial groups,which were related to soil carbon and nitrogen cycles.The dominant groups of the phyllobacterial network in vegetable maize were Proteobacteria,Bacteroidetes and Firmicutes,while the dominant groups of the bacterial network in vegetable maize rhizosphere and rhizosphere soil were Proteobacteria,green Flexobacteria,Firmicutes,pontomyces and Bacteroidetes.Fertilization reduced the complexity of vegetable maize bacterial network,possibly because fertilization lost some key rare species that were not dominant taxa.Proteobacteria,Firmicutes,and Actinomycetes are common dominant groups in culture and non-culture mode.This study revealed the effects of nutrient imbalance on bacterial community composition and diversity in different ecological niches of vegetable maize at different growth stages,which provided theoretical reference for clarifying the response of bacteria to fertilization management measures in vegetable production and adopting microbial strategies to better cope with nutrient imbalance stress.