Study On The Controlling And Mechanism Of Functional Consortia On Pb/Cd Uptake In Wheat

Heavy metal pollution on farmland is becoming increasingly prominent with atmospheric deposition,industrial wastewater,inappropriate use of pesticides and fertilizers,etc.Microbial remediation,as a promising remediation technology,is widely used for heavy metal control in agricultural fields.However,for farmland heavy metal remediation,most of the current studies focus on single functional microorganisms,fewer studies have been conducted to design microbiome for remediation of heavy metal contaminated soils based on single microbial properties by bottom-up approach.In this study,we selected 10 functional microorganisms with heavy metal resistance,analyzed their functional characteristics and used them to construct functional consortia,and the effects of functional consortia on soil microbial activity,Pb/Cd speciation and the composition and structure of bacterial community during wheat heading and maturity stages were analyzed through indoor pot experiment.Further,we explored the response of wheat growth to functional consortia and revealed the control mechanism of Pb/Cd uptake in wheat by functional consortia.The main results of the study are as follows:(1)The test strains were characterized and three functional consortia were constructed.Based on the probiotic function(the ability of indole acetic acid production,phosphorus solubilization,siderophore production)and Pb/Cd removal function of the test strains,three types of functional consortia with different functional levels were synthesized by the "bottomup" approach: strong-associated(Con-A),complementary(Con-B)and weak-functioning(Con-C).(2)The effect of functional consortia on soil enzyme activity,microbial biomass,nutrient content,and Pb/Cd speciation were investigated.The functional consortia increased soil enzyme activity and microbial biomass,and the effect of Con-B was more significant at wheat heading stage,which increased rhizosphere soil catalase,phosphatase and invertase activities(5.7%,10.4% and 3.5%)and increased the content of microbial biomass carbon,nitrogen and phosphorus in rhizosphere soil(36.9%,57.0% and 34.6%).Con-A has a greater effect at wheat maturity stage.The functional consortia increased soil p H,organic carbon,and decreased DTPA-Pb/Cd content.Further,it was found that the functional consortia decreased the proportion of acid soluble state and reducible state,meanwhile,increased the proportion of residual state,among them,Con-A and Con-B have the greater impact on Pb,Cd speciation,and Con-C has the smaller impact.(3)The effect of functional consortia on bacteria community composition and structure of rhizosphere soil was revealed.The dominant bacteria populations of rhizosphere soil during both wheat heading and maturity stages were mainly composed of Proteobacteria,Bacteroidetes,Acidobacteria,and Actinobacteria,and inoculation of the functional consortia increased Patescibacteria relative abundance,but Actinobacteria relative abundance was decreased.Inoculation of functional consortia increased bacterial community richness and diversity in the short term and decreased after long-term incubation,and the bacterial communities differed significantly under different functional consortia.At the heading stage,the bacterial community was more correlated under Con-B than Con-A treatment at the phylum level,while at the maturity stage,the interactions were closer under Con-A treatment.(4)The effect of functional consortia on wheat growth and Pb/Cd uptake were clarified.Inoculation of functional consortia significantly increased plant height,biomass,root growth,the content of chlorophyll and nutrient.Con-A and Con-B significantly increased antioxidant enzyme activities in wheat leaves and roots,and reduced oxidative damage in wheat.At the wheat heading stage,inoculation with Con-B had a more significant effect on Pb/Cd blocking and reduced Pb/Cd content in all tissues of wheat and Pb/Cd enrichment in the ear.At the maturity stage,Con-A reduced the Pb/Cd content in wheat grain more significantly compared with Con-B and Con-C,and reduced the Pb/Cd content in wheat grain by 22.9% and 5.9%,respectively.(5)Further,the regulatory mechanism of the functional consortia on wheat growth and Pb/Cd uptake was parsed based on the partial least squares path model(PLS-PM).The functional consortia promoted wheat growth by significantly increasing antioxidant enzyme activity and reducing biological availability of Pb/Cd in soil,alleviating Pb/Cd stress in wheat,secreting metabolites,and promoting plant growth eventually.At the same time,the functional consortia enhanced the fixation of Pb and Cd in the soil by improving soil biochemical properties and nutrients,and regulated the migration and transport of Pb and Cd in the soilwheat system,which ultimately reduced the uptake of Pb/Cd in wheat.