Rhizosphere Microbiome Analysis And Selection And Construction Of Growth-Promoting Flora Of Maize And Soybean Under Single And Intercropping Mode

The intercropping pattern of soybean and maize is a widely used agricultural cropping system,in which the rhizosphere microorganisms and root secretions are located in the rhizosphere micro-ecosystem where frequent material and information exchange is occurring.In this study,we investigated the composition and function of the rhizosphere microbial community and the metabolome of the plant root system under monoculture and intercropping patterns of soybean and maize at different fertility stages.At the same time,root secretions of corn and soybean under different cultivation methods were collected and measured to find the relationship between root secretions and the rhizosphere microflora.Finally,the probiotic strains with significant growth-promoting effects were selected and optimized to build a synthetic flora.The main results are as follows:(1)The results of phenotypic and physiological indexes of soybean and maize sampled and analyzed in monoculture and intercropping patterns at 15 d,45 d and 65 d after sowing showed that plants generally grew better in the intercropping pattern compared with monoculture.In particular,at 65 d,the intercropping pattern increased plant biomass and promoted the formation of soybean root nodules.(2)The results of plant and soil nutrient content measurements showed that the intercropping pattern promoted the uptake and utilization of soil nutrients by soybean and maize,and the phosphorus and potassium contents of intercropped plants showed an overall increasing trend compared with monocropping;however,in terms of nitrogen,the nitrogen content of intercropped soybean showed a decreasing trend compared with monocropping,especially at 45 d,while maize showed the opposite trend,indicating that the intercropping system This may have caused nitrogen deprivation in soybean,thus promoting the formation of symbiotic root nodules.Soil N,P,and K contents generally decreased with plant growth period,indicating that they were absorbed and utilized by plants during the period;compared with monoculture,nitrate N,fast-acting potassium,effective phosphorus,and organic carbon contents of intercropped soils decreased to different degrees during the same sampling period,indicating that the intercropping pattern promoted the uptake and utilization of soil nutrients by soybean and corn.(3)High-throughput sequencing analysis of rhizosphere soil samples from different cropping patterns yielded 24,320 soil ASVs.microbial diversity and microbial composition analysis revealed that different cropping patterns and different sampling time points had significant effects on soil microbial communities.In the monoculture model,both soybean and corn were significantly enriched in Proteobacteria and Acidobacteria in the inter-rhizosphere.Meanwhile,Chloroflexi and Bacteroidota were significantly higher in soybean and corn under45 d and 65 d intercropping systems than in monoculture.The results of rhizosphere differential microbial analysis showed that soybean was enriched with Sphingobacterium,Pseudoxanthomonas,and UTCFX1 genera in the intercrop mode and Lysobacter,Sphingomonas,and Pseudarthrobacter in the monocrop mode;corn was enriched with The results of the rhizosphere microbial co-occurrence network analysis showed that both soybean and maize were enriched in the intercropping mode with Flavisolibacter,Stenotrophomonas,and Variovorax,and Bryobacter,Sphingomonas,and Arenimonas in the monocropping mode.The results of the rhizosphere microbial network analysis showed that the rhizosphere microbial network was more complex than that of the monocrop in both soybean and maize.The core microorganisms were screened by intramodule connectivity(Zi)and inter-module connectivity(Pi)analysis of each node in the cogenerative network and belonged to the phyla Actinomycetes,Aspergillus,and Phytophthora,respectively.(4)The analysis of soil N cycle functional genes showed that the abundance of nitrification-related genes was up-regulated in intercropping compared with monocropping,while the abundance of denitrification-related genes was mostly down-regulated in intercropping,presumably enhancing the conversion of nitrite to nitrate in soil and possibly inhibiting the denitrification process.(5)A total of 2249 substances,mainly sugars,organic acids,and amino acids,were detected from root secretions by metabolomics analysis.After annotation of differential metabolites in different cropping patterns,soybean roots were enriched in metabolites such as Enoxolone,Ademetionine,and methadone-d9 in the intercrop pattern,while maize roots were enriched in metabolites such as Acetophenone,Daidzein,and Heptamethoxyflavone.After correlation analysis of differential metabolites and differential microorganisms obtained by comparing monocultures and intercrops of the same plant species under the same sampling period,it was found that microorganisms of genera such as Sphingobacterium and Bacillus were significantly correlated with various root metabolites such as N-Acetyl-DL-valine,Polygalic acid,etc.in soybean.And microorganisms of genera such as Flavisolibacter and Pseudorhodoferax in maize inter-rhizosphere soil were significantly correlated with various root metabolites such as Nicotianamine and Bruceine D.(6)284 strains were isolated from the above-mentioned inter-rhizosphere soil and preliminary species identification was performed.Using the results of inter-rhizosphere microbiome analysis under different cropping patterns as a guide and combined with the strain growth-promoting performance testing,eight strains of growth-promoting bacteria were screened,belonging to the genera Stenotrophomonas,Ensifer,Kosakonia,Pseudomonas,Leclercia,Bacillus and other genera,and combined them into two synthetic bacterial groups.The two synthetic colonies were inoculated with soybean,corn and wheat under natural soil conditions,and the results showed that both colonies had different degrees of growthpromoting effects on all three crops.In summary,this study provides a preliminary investigation into the microbiological mechanisms of soybean and corn intercropping patterns to enhance crop growth through the analysis of growth indicators,elemental content,rhizosphere microbiome and root secretions under different cropping patterns,and provides a reference for the comprehensive analysis of rhizosphere microecological processes under intercropping patterns,as well as how to enhance rhizosphere microecological functions to improve soil health under monoculture patterns.It also provides a reference for improving soil health under monoculture by enhancing rhizosphere microecological functions.