Effects Of Straw Compost And Plant Rhizosphere Synthetic Community On Soil And Maize Growth

Crop straw is an important biomass resource,which is rich in nitrogen,phosphorus and potassium.About 40.0%of straw is burned every year,causing serious resource waste and air pollution.Straw return is widely used as an eco-friendly treatment method,but in practice it interferes with crop cultivation,harbors pathogens or pests,and immobilizes nutrients in the soil and fertilizer.In previous study,high temperatures and various microbial-mediated biochemical processes during composting can destroy pathogens and recover nutrients,but few studies have been reported on the straw compost return.In this study,0,2.5,5 and 7.5 t/hm~2 of straw compost were mulched and buried to investigate the effects on soil physicochemical properties,microbial community structure and physiological indicators of maize,and then to identify the best way to return to the field and the key factors for maize yield improvement.The plant growth-promoting rhizobacteria(PGPR)were screened from maize rhizosphere soil in the straw compost plots.The PGPRs colonized on maize root were constructed into a synthetic community through the interaction between strains,and then the growth promoting mechanism of the synthetic community was elucidate.The main findings were as follows:Straw compost had no effect on soil chemical properties,but significantly improved soil agglomerates structure,especially 7.5 t/hm~2 mulching treatment reduced the content of>2 mm mechanically stable agglomerates in the soil at the flower period.Meanwhile,bacterial community structure responded more significantly to straw compost than fungal community structure.In the process of straw compost,straw compost mulching treatment enhanced maize yield,while 7.5 t/hm~2 mulching treatment had the best effect on corn yield enhancement.Therefore,the best return method was mulching treatment and the concentration was 7.5 t/hm~2.At the family level,two fungi(Trichocomaceae and Didymellaceae)and five bacteria(Xanthomonadaceae,Rhizobiaceae,Micrococcaceae,Micromonosporaceae and Microbacteriaceae)and>2 mm mechanically stable agglomerates were significantly associated with the yield enhancement.All environmental factors could explain 81.36%of the yield enhancement.Among them,the contribution of Xanthomonadaceae,Rhizobiaceae and>2 mm mechanically stable agglomerates was greater than that of other environmental factors.Bacterial community structure as a key factor for yield enhancement.Then,A total of 20PGPR strains of different genera were screened in the rhizosphere soil.A strain belonged to Rhizobiaceae and the remaining 19 PGPR strains belonged to Bacillaceae,Sphingomonadaceae,Moraxellaceae,Pseudomonadaceae and Enterobacteriaceae.All 20 PGPR strains have the ability to secrete IAA,gibberellin,phosphate,potassium and nitrogen fixation,and then significantly promote plant growth.However,only Pseudomonas hunanensis SM15,Enterobacter huaxiensis SM16,Klebsiella pneumoniae SM17 and Klebsiella granulomatis SM18 were able to colonize on the root system of maize.A synthetic community consisting of Priestia aryabhattai SM03,Acinetobacter guerrae SM12,Klebsiella pneumoniae SM17 and Klebsiella granulomatis SM18 was constructed and the effect of the synthetic community on the bacterial community of maize roots was higher than that of the soil microbial community in rhizosphere soil.Meanwhile,Klebsiella,a member of the synthetic community,colonized on the maize root system as the dominant genus with a relative abundance of 30%.Moreover,microbial functions were associated with cell proliferation on day 3 of inoculation with the synthetic community,while day 30 was associated with soil microbial nutrient conversion and antimicrobial production.Additionally,the plant hormone signal transduction as a key pathway related to plant growth and development,and the key genes involved in this pathway(AUX/IAA,SAUR,ARR-B,ABF,ERF1,TCH4,JAZ,and PR-1)were up-regulated.In summary,straw compost mulching treatment significantly enhanced maize yield by optimizing soil agglomerates structure and improving disease resistant microbial community structure.This study has important scientific significance and practical application value for solving the environmental pollution problems caused by straw burning and ensuring people’s food security.