Interactions Between Winter Wheat And Rhizosphere Microorganisms During Drought Stress

Wheat,as one of the world’s most three major cereal crops,however,environmental factors such as drought heavily impact wheat production.The rhizosphere serves as a vital interface for root-soil-microbe interactions,where rhizosphere microbial activities can influence various aspects of plant nutrition absorption,hormone synthesis,pathogen defense,and physiological metabolism,holding significant potential in enhancing plant drought resistance.Investigating the impact of drought stress on rhizosphere microbial community composition,microbial interaction,and plant-microbe interaction is of paramount scientific importance in revealing the mechanisms and dynamics of microbial community construction in dryland agricultural soil and their feedback on plant growth.The North China Plain is the largest winter wheat grain-producing region in China,but it is frequently affected by drought.This study focuses on winter wheat fields in Hengshui city,Hebei Province,employing a combination of in-situ experiments and contemporary molecular biology techniques.It aims to investigate the effects of drought on the rhizosphere microbial community and functions in winter wheat fields,exploring the feedback effects of microbial community changes on plant growth.This comprehensive study contributes to understand the response of rhizosphere microbial communities to drought stress and the relevant functional microbial populations that can enhance plant drought resistance.The primary research findings can be categorized into the following four parts:(1)By utilizing high-throughput sequencing,we conducted a study on the bacterial communities in bulk soil,rhizosphere,and root of winter wheat farmland soil in the North China Plain.We found that the host plant exerted a strong selective effect on the rhizosphere and root bacterial communities,leading to a reduction in the community’s alpha diversity index.The bacterial communities were influenced by drought stress,especially the root bacterial communities,with a significant decrease in Shannon and Chao1 indices during drought stress.NMDS analysis revealed that drought had a more pronounced impact on the structure of rhizosphere and root bacterial communities compared to bulk soil.In comparison to the control,there was minimal variation in the bacterial communities of bulk soil under drought stress.Drought stress affected the composition of bacterial communities,elevating the relative abundance of Actinobacteria in both bulk soil and rhizosphere,while the relative abundance of alpha-Proteobacteria increased in root.Differential analysis also indicated that under drought stress,the majority of significantly enriched genus in bulk soil and rhizosphere belonged to the Actinobacteria phylum,while in the root,they belonged to the Proteobacteria phylum.Network analysis demonstrated that the average degree of both rhizosphere and root bacterial networks were lower than those in the bulk soil.With increasing drought severity,the average degree index of the rhizosphere network gradually decreased,whereas the root network decreased during mild drought stress and increased during moderate drought stress.Through analyzing the changes in various modules in the network under drought stress,we identified a key microbial group significantly associated with winter wheat yield.This group included Actinobacteria genus that were significantly enriched under drought conditions,with their relative abundance notably increased in both rhizosphere and root during drought stress.(2)Analysis of the fungal communities in the bulk soil and rhizosphere of winter wheat fields in the North China Plain revealed that host selection influenced the construction of rhizosphere fungal communities.NMDS and PERMANOVA analyses indicated that host selection and drought stress both affect the fungal communities.Functional predictions using FUNGuild revealed differential impacts of drought on the composition of bulk soil and rhizosphere communities,significantly increasing the relative abundance of saprotrophic fungi,with no significant differences observed in bulk soil.Network analysis uncovered that drought enhanced the average degree of the fungal network in bulk soil,while reducing it in the rhizosphere network.Under drought conditions,the edges associated with saprotrophic fungi decreased in the bulk soil network and increased in the rhizosphere network.Furthermore,it was observed that the species enriched in rhizosphere under drought stress mainly belonged to the saprotrophic fungi,with OTU164 exhibiting the highest abundance,but showed no significant difference in bulk soil.A strain was isolated from rhizosphere soil,sharing high sequence similarity with OTU164 and named Chaetomium sp.DR413;inoculation with DR413 revealed its promotion on winter wheat growth under drought stress,primarily manifested in root elongation.RT-q PCR analysis of fresh root RNA showed that DR413 significantly increased the expression of ABA signaling pathway genes,which were significantly correlated with plant root length.(3)In pot experiments,this study investigated the rhizosphere bacterial and fungal communities and their interactions at different growth stages of winter wheat during drought stress,including tillering,jointing,and maturity stages.The findings revealed that drought had negative effects on winter wheat growth at all growth stages,significantly reducing plant height and weight.Rhizosphere bacterial and fungal communities responded differently to drought at different growth stages.The bacterial communities exhibited a significant decrease at the tillering and jointing stages but showed no significant difference at the maturity stage.Analysis of microbial community stability indicated that drought reduced the stability of both bacterial and fungal communities at the tillering and jointing stages and the overall stability of the fungal communities at all three stages.The growth stages of plants had varying effects on bacterial and fungal networks.Compared to the tillering stage,the average degree and stability of bacterial and fungal networks increased and decreased at the jointing and maturity stages,respectively.Drought stress increased the average degree and stability of both bacterial and fungal networks.Constructing a bacterial-fungal interaction network revealed that the proportion of interactions between bacteria and fungi was higher at the jointing stage than at the tillering stage.Under drought stress,the proportion of bacterial-fungal interactions increased.Finally,module analysis of the network unveiled a key module closely related to plant development,with a relatively high proportion of fungi,indicating that an increased proportion of bacterial-fungal interactions in the rhizosphere microbial network is conducive to the development of the plant host.(4)Using the dilution-to-extinction method,the microbial diversity communities with different dilution gradients were built,which significantly reduced alpha diversity of rhizosphere bacterial communities.However,the impact of dilution levels on the diversity of root bacterial communities was mediated by the host and drought stress.Dilution only suppressed the plant height and biomass of winter wheat under drought stress,without significantly negative effects on the growth of winter wheat in control treatments.Furthermore,the diversity of rhizosphere bacterial communities under drought stress was significantly correlated with the biomass of winter wheat.Both drought and dilution levels significantly affected the structure of both rhizosphere and root bacterial communities.In the rhizosphere,drought led to an increase in the relative abundance of Actinobacteria in the undiluted treatment,while the diluted treatment resulted in a decrease in the abundance of Actinobacteria species,with their relative abundance significantly negatively correlated with the dilution level and positively correlated with the biomass of winter wheat.Differential analysis indicated that under drought stress,the significantly enriched species in the undiluted rhizosphere treatment were mostly Actinobacteria species,a phenomenon that disappeared in the diluted treatment.Moreover,dilution also resulted in changes in the function of bacterial communities under drought stress.The construction of a bacterial network revealed the existence of a key ecological cluster significantly associated with the biomass of winter wheat,mainly composed of Actinobacteria species,only in the rhizosphere treatment under drought stress.However,their abundance decreased with an increase in the dilution level.These findings suggested that the reduction of microbial diversity may lead to the extinction of beneficial functional microbes in the soil,inhibiting the recruitment of these microbes by the host plants,consequently limiting plant growth under drought stress.