Effect Of Alkali-producing Microbial Compound Inoculant On Rice And The Mechanism

With increase of population and development of social economy,heavy metal pollution in soil is becoming more and more serious,and remediation of contaminated soil has become focus of attention.Traditional physicochemical remediation and bioremediation often have limitations and instability.The combined remediation means coordinating two or more remediation methods for soil remediation,not only makes up the shortcomings of traditional remediation,but also improves the remediation effect,which has gradually become the mainstream of remediation of contaminated soil.In this thesis,using the alkaliproducing microorganisms combined with passivators to treat cadmiumcontaminated agricultural soils,then analyzing the effects on rice growth and soil available cadmium,and its mechanism was explored.The main studies as follows:Firstly,three alkali-producing strains named Ls,Lg and DQ-2 were screened from the alkaline environment of Hunan.The identification of microorganisms,optimization of growth conditions and biological characteristics of three alkali producing strains were studied.They had biological characteristics of alkali production,and the p H of their growth medium could reach 8.20,8.39 and 8.29,respectively(initial p H is 7.23).It has found that they belong to Citrobacter sp,Enterobacter sp,and Micrococcus sp,respectively by morphological observation,physiological and biochemical identification and 16 S r DNA sequence analysis.Their growth cycles were 44,40 and 44 h,respectively,and the optimal growth conditions were carbon source: peptone,nitrogen source:yeast,and initial p H: 6.50.In addition,they could immobilize cadmium in contaminated soil,and the soil available cadmium content decreased by 50.13%,56.11%,52.41%,respectively.Secondly,the effects of biochar,sepiolite and hydroxyapatite passivators on soil and growth of Lg strains were studied.The results showed that three kinds of passivators all could improve farmland soil p H value,and 2% passivator had the best effect.The soil available cadmium decreased by 4.31% and 19.67% in sepiolite and hydroxyapatite treatment groups,respectively,while biochar treatment group was increased when 2% passivators were inoculated to contaminated farmland soil after 48 h.When combined with Lg strains to treat farmland soil,and immobilization efficiency increased after 48 h.Among them,hydroxyapatite combined with Lg strains could maximize decrease soil available cadmium,up to 69.01%.The effects of hydroxyapatite combined with Lg strains(alkaliproducing microbial inoculant)on rice growth and cadmium accumulation,as well as soil available cadmium were analyzed under outdoor rice pot experiment.Compared with CK group,it could improve the grain quality and quantity,plant height,and rice seed setting rate by27.27%,22.81%,5.00% and 3.62%,respectively.It also could decrease cadmium content in grain and straw by 79.69% and 25.07%,respectively.In addition,it could reduce soil available cadmium in contaminated soil by up to 47.75%.The effects of alkali-producing microbial inoculant on the expression of different cadmium transporter genes(Os HAM2,Os HAM3,Os NRAMP1,Os NRAMP1 and Os ZIP4)at different times of rice were investigated by real-time PCR under indoor rice pot experiment.The results showed that five cadmium transporter genes expression changed and the influence increased with time.On the 15 th day of treatment,five cadmium transporter genes expression were down-regulated 4.53-fold,5.34-fold,5.37-fold,4.53-fold and 5.41-fold,respectively.In addition,the difference in up-and down-regulation differences of Os NRAMP1 and Os HAM2 genes expression was higher than other cadmium transport genes.Therefore,it was speculated that the inoculant might affect cadmium uptake in rice by up-and down-regulating Os NRAMP1 and Os HAM2 genes at different periods of rice growth,and assisted by other cadmium transport genes.Finally,Ls,Lg and DQ-2 strains combined with hydroxyapatite were used to prepare alkali-producing microbial compound inoculant for treating outdoor potted rice.The results showed that this compound inoculant could reduce soil available cadmium in contaminated soil by7.17%.Compared with CK group,it could reduce cadmium content in grain by 41.19%,and improve growth state of rice.In addition,comparing microbial communities in the two periods,it was found that this compound inoculant had no significant effect on the diversity of soil microbial communities.Soil microbial community had significant difference in phylum classification,but this difference was affected by soil Cd concentration.