Effects Of Rhizosphere Microbiomes On Volatile Organic Compounds And Crop Growth

With the increasing problems of resources and environment,many scholars began to explore effective ways to achieve green and sustainable agricultural development from the plant-microbial interaction.The rhizosphere is a hot zone of plant-soil-microbe interaction.Rhizosphere microbes are the most active participants and closely related to plant growth and development,nutrient uptake,and biotic and abiotic resistance.Plant-microbial interaction involves a wide range of signal transduction.Volatile organic compounds,as a special signal substance,play an important regulatory role in rhizosphere interaction and have broad application prospects in agriculture.This study utilizes dryland ploughed soils in six regions including Dezhou(DZ),Laishui(LS),Quyang(XL),Nanchang(NC),Mengjin(MJ),Shangqiu(SQ),and the sterilized Fluvo-aquic soil inoculated with different microbial communities to carry out the maize pot experiment.The VOCs emitted from maize rhizosphere were identified by solidphase microextraction(SPME)fiber and gas chromatography-mass spectroscopy.Real-time quantitative(qPCR)and high-throughput sequencing technology were used to determine the differences in bacterial and fungal communities.We analyzed and compared the microbial community characteristics and volatile organic compounds in different rhizosphere soil,and tried to explain the effects of rhizosphere microbial community on crop growth from the aspects of soil enzyme activity,root phytohormone and volatile organic compounds.The research results are as follows:1.A total of 44 VOCs were detected,belonging to alkanes,alkenes,esters,amines,organic acids and aromatics.Many of these compounds were closely related to the growth and metabolism of plants or microorganisms.Two amine compounds,N-Benzyl-N-ethyl-p-isopropylbenzamide and D-2-Bromolysergic acid diethylamide,were detected in all treatments,accounting for 54.2% of the total.The second and third abundant VOCs were alkanes and alkenes,accounting for 31.1% and 7.6% of the total,respectively.The VOCs released from NC were significantly higher in number and richness than other treatments,and most of them were alkanes and olefins.Six unique organic acids and esters were detected from XL.Among the six soils,the abundance of bacteria in SQ and XL was significantly higher than others,and the abundance of fungi in NC was significantly higher than others,but the abundance,richness and diversity of bacteria in NC were significantly lower than those in other soils.The main bacteria in the six soils were Thaumarchaeota,Actinobacteria,Proteobacteria,Chloroflexi,Acidobacteria,Firmicutes.Phytophthora and Unclassified,accounted for 92.1% of the total bacterial community.The main fungi were Ascomycota,Basidiomycota and Chytridiomycota,accounting for 98.3% of the total fungal community.Chloroflexi only accounted for an absolute advantage in the NC,but the relative abundance of the Thaumarchaeota and Proteobacteria in NC was significantly less than those in other soils;Ascomycota was an absolutely dominant fungi in all six soils.The number and richness of VOCs released from rhizosphere of maize were significantly negatively correlated with pH,nitrate nitrogen,bacterial diversity and fungal diversity(P<0.05),and significantly positively correlated with ammonium nitrogen and the number of fungi(P<0.01).The VOCs were significantly negatively correlated with the relative abundances of Thaumarchaeota,Proteobacteria and Acidobacteria(P<0.05),and positively correlated with the Chloroflexi(P<0.01),but the correlation with the main fungal gate was not significant.2.Under the influence of soil type,initial microbial community and plant roots,soil microbes could aggregate in the rhizosphere of maize to form rhizosphere microbial communities dominated by Proteobacteria,Bacteroidetes,Acidobacteria,Firmicutes,Chloroflexi,Actinobacteria,Planctomycetes,Verrucomicrobia and Ascomycota.and significantly affects maize growth.The number of bacteria and fungi in the rhizosphere,the diversity of bacteria and fungi communities,and the structure and composition of the bacteria and fungi all affected the growth of maize and the nutrient accumulation of maize plants at varying degrees.Rhizosphere bacterial abundance,bacterial and fungal community diversity were significantly positively correlated with LAP and AP activity.Proteobacteria,Acidobacteria and Thaumarchaeota also showed a positive correlation with soil enzyme activity.In this study,19 different kinds of phytohormones were detected from the roots of maize by HPLC-MS/MS.The contents higher than 1ng/g were JA,IAA,ABA,SA,ICA and CZ.Among them,14 hormone contents were significantly correlated with rhizosphere microbial community diversity or population abundance.Among 89 kinds of VOCs detected from maize rhizosphere soil,there were 19 species with relative abundance greater than 1%,and 17 kinds of VOCs were significantly correlated with rhizosphere microbial community diversity or population abundance.In addition to directly affecting the nutrient uptake by crops,rhizosphere microorganisms may affect crop growth by increasing soil enzyme activity,directly or indirectly regulating the content of different phytohormones in crop roots and the production and release of soil VOCs.However,due to the complexity of the crop rhizosphere environment,the interrelationship and molecular mechanism of these various pathways has yet to be further studied.