Diversity Of Soil Microorganisms In Grain Fields And Their Effects On Millet Effects Of Physiology,biochemistry And Yield

Soil is the most important component of agro-ecosystems and the basis for crop's survival.Soil fertility is the main factor affecting crop yield,and soil microorganisms are vital part of soil biomass.Soil microorganisms in plant rhizosphere play an important role in improving soil fertility and promoting healthy growth of crops.Soil nutrients,soil enzyme activity and soil microbial diversity are important indicators of soil fertility in plant rhizosphere.In recent years,with the application of high-throughput sequencing technology,the study of microbial diversity in rhizosphere soil and the role of functional microorganisms in soil have been gradually confirmed.Microorganisms in soil participate in the cycling of soil nitrogen(N),phosphorus(P)and potassium(K),the decomposition and utilization of soil organic carbon(SOC)and the inhibition of soil-borne diseases.In addition,some soil microorganisms as plant pathogenic bacteria cause crop diseases.As an important cereal crop,millet(Setaria italic)is characterized by infertility resistance,drought resistance and strong stress resistance.It is often used as a pioneer crop for soil improvement in arid and semi-arid regions of northern China.This study mainly took the rhizosphere soil of millet(Setaria italic)as the research object,and used the millet yield as the index to measure the soil nutrient and microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN)in the rhizosphere soil of millet under different management modes and land use patterns.In addition,agronomic characteristics,photosynthetic index and antioxidant enzyme activity were determined;16S r DNA high-throughput sequencing analysis was performed on all treated soil samples;fungal diversity analysis was added to soil samples in rotation mode;The 16 S r DNA,Pseudomonas spp.,nif H,nir S,and nir K genes of bacteria in all samples and ITS region and of fungi in rotation soil were detected by real time fluorescence quantification PCR(q PCR).The main findings are as follows:First,The effects of different fertilization treatments on the rhizosphere soil of millet showed that compared with no fertilization group,N,P,K and organic fertilizer combined application(NPKM)had the highest yield;the highest content of available nitrogen(AN),AP,SOC,MBC and MBN;the highest C/N value.The abundance of specific bacteria increased,at the level of the phylum were Actinobacteria and Bacteroidetes;at the level of genus were Devosia,Mycobacterium,Opitutus and Chitinophaga.Redundancy analysis(RDA)reveals that AN was highly positively correlated with Devosia and Mycobacterium;SOM was significantly associated with Opitutus and Chitinophaga.The q PCR results showed a significant increase in the abundance of the nif H,nir S and nir K genes.This indicates that the application of nitrogen and organic fertilizer promotes the proliferation of nitrogen-fixing bacteria and the increase of bacterial community diversity in soil,and increased soil enzyme activity and millet yield.Second,the results of research on the cultivation of millet in immature soil(IS),mellow soil(MS)and the mixture of MS and IS(MSIS)showed that compared with IS,AN,AP,SOC,MBC and MBN contents,C/N and MBC/MBN values in MS were the highest,the millet yield was also the highest.The abundance of specific bacteria increased,at the level of the phylum were Proteobacteria and Actinobacteria;at the genus level were Caenimonas,Gemmatimonas,Lysobacter,Ramlibacter,Devosia,Mycobacterium and Streptomyces,and RDA showed that these 7 genera were highly positively correlated with SOC,AN and C/N.PCR results showed a significant increase in the abundance of nif H gene.We speculate that these bacteria can be involved in the N cycling.Third,the effects of different rotation patterns on agronomic characteristics and physiological and biochemical characteristics of millet: Compared with continuous cropping millet,Malondialdehyde(MDA)decreased after millet(Setaria italica,Si)-Soybean(Glycine max,Gm)-Potato(Solanum tuberosum,St);millet yield,plant height,ear length and thousand-grain weight increased;stomatal conductance,Photosynthetic rate,transpiration rate and relative chlorophyll content increased;polyphenol oxidase,superoxide dismutase and peroxidase activities increased;the incidence rate of downy mildew of millet decreased.Fourth,the effects of different rotation patterns on millet soil showed that compared with Si,Si-Gm-St significantly increased levels of soil AN,AK,TK,C/N,BMC and BMN,and the activity of soil alkaline phosphatase and polyphenol oxidase.Studies on bacterial diversity have found that the relative abundance of Actinobacteria,Proteobacteria,Gemmatimonadetes,Chloroflexi and Cyanobacteria in Si-Gm-St increased compared with continuous cropping;the relative abundance of some bacteria genera Pseudomonas,Lysobacter,Devosia,Acidovorax and Agromyce Increased;RDA showed that these five genera were highly positively correlated with C/N,AP,AN and SOC;Pearson analysis showed that the relative abundance of Pseudomonas was significantly negatively correlated with the incidence rate of downy mildew of millet.q PCR showed that the abundance of the bacterial Pseudomonas spp and nif H genes was significantly higher in the Si-Gm-St than in the rotation.The results of fungal diversity analysis showed that compared with continuous cropping,at the level of phylum,the relative abundance of Basidiomycoda in the rhizosphere of millet in Si-Gm-St decreased;at the level of genus,the relative abundance of Buergenerula,Rhizophlyctis,Ophioceras,Cyathus,Preussia,Acremonium and Ilyonectria increased.The results of q PCR showed that after rotation,the ratio of fungi to bacteria decreased,the fungal diversity,the abundance and diversity of bacteria increased.This indicates that the less soil pathogenic bacteria in rotation which is more conducive to the health of crops.