Assembly Of Root-associated Microbiomes Of Rice(Oryza Sativa L.) In Response To Lindane Pollution

Microbial communities associated with plant roots?defined as root-associated microbiomes?are conducive to plant growth,nutrient uptake and stress resistance.In recent years,with the development of biotechnology,researches on the assembly of root-associated microbial communities have gradually become a global focus.China is the most important producer and consumer of rice around the world,exploring the assembly of root-associated microbiomes of rice and clarifying the mechanisms of the influencial factors are important for ensuring food security and maintaining the stability of the rice field ecosystem.Lindane??-Hexachlorocyclohexane,?-HCH?is an organochlorine pesticide?OCP?which is easy to be accumulated in soils due to the difficulty in degrading,thereby posing potential risks to the underground ecological environment.In the long-term flooded environment of rice planting,the reductive dechlorination of lindane is closely coupled with the cycle of biogenic elements in the soil.In this research,we take lindane as a typical representative of OCP,and rice as the main research object.A combination of high throughput sequencing technology,quantitative PCR technology,and accelerated solvent extraction technology are used for investigating the structure and function of root-assciated microbiomes of rice,the regulation effect of root characteristics under pollution stress,and the ecological response of root-assciated microbiomes to pollution stress driven by alternate wet and dry conditions?AWD?.Finally,we combined rice and typical dry farming plants to explore the microbiological mechanisms for self-purification of lindane polluted soil during plant growth.The main research results obtained are as follows:1. The bacterial 16S rRNA gene sequencing technology was used to study the composition and spatio-temporal dynamics of root-associated microbiomes of rice in two different soil types.The results showed that soil types,rice growth time and rhizo-compartment had significant effects on the microbial communities.The contribution of lindane on the assembly of root-associated microbiomes was least,but it played an important role in regulating microbial responses in specific environments.Lindane pollution significantly promoted the microbial diversity in rice roots during the vegetative growth phase,and affected the microorganisms involved in the complex redox coupling of the reductive dechlorination of lindane in rhizosphere soils.2. Fungal ITS and bacterial 16S rRNA gene sequencing technology were used to study the functional differences and ecological effects of microorganisms under lindane stress.The results showed that lindane pollution had less effect on the root-asscoiated fungal communities of rice,but it significantly increased the relative abundance of Bacillaceae and Comomamonadaceae in the rhizosphere soil.Rice growth significantly inhibited the dissipation of high-concentration lindane in flooded anaerobic environment.The hybrid rice had a less inhibitory effect and a more stable rhizoshere microbial community than that of conventional cultivars under pollution stress.3. The bacterial 16S rRNA gene sequencing technology was used to study the regulation of microbial community structure by iron plaque in rice root surface under lindane pollution.The results showed that affected by the oxidative characteristics of rice roots,changes in oxidative conditions around the roots may strengthen the coupling between the reductive dechlorination of lindane and the redox processes of iron,resulting in the variation of composition and diversity of root-associated microbiomes of rice.Lindane pollution mainly reduced the diversity of microbial communities of rhizoplane and changed the ecological network of the microorganisms in this area;the enrichment of iron plaque significantly reduced the promotion effect of pollution stress on the microbial diversity in rice roots,and it affected the tropismal migration of microorganisms such as Magnetospirillum from the root to the rhizoplane and changed the ecological network of endosphere.4. The 16S rRNA gene sequencing technology of archaea and bacteria were used to study the response mechanisms of root-associated microbiomes to lindane pollution driven by the wet and dry alternation?AWD?.The results showed that AWD process caused changes in soil redox conditions and physiochemical properties;it also significantly changed the relative abundance of Enterobacteriaceae,Desulfarculaceae,Geobacteraceae,Moraxellaceae and other microorganisms in different rhizo-compartments of rice roots,and affected the relative abundance of lindane degrading bacteria such as Streptomyces and some functional microorganisms such as Nocardioides and Geobacter,which were capable of mediating the soil redox processes in this short-term aerobic period,and thus significantly inhibit the degradation rate of lindane during the AWD process.5. The bacterial 16S rRNA gene sequencing and q PCR technology were used to comparatively study the differential responses of root-associated microbiomes of maize,soybean and rice to lindane stress.The results showed that lindane pollution showed no obvious effect on the microbial populations of maize and soybean,but significantly changed the abundance of microorganisms such as Sphingomonas and Streptomyces.Affected by the characteristics of plant roots and their effects on the rhizosphere soils,the growth of maize and soybean significantly promoted the degradation of lindane,but the dissipation rates were obviously different.However,due to the influences of root O₂ secreting characteristics and the root-assocaited microbiomes,rice planting significantly inhibited the dissipation of lindane in the rhizosphere soils.Based on the above results,we found that soil types play a leading role in regulating the assembly of root-associated microbiomes of rice.Different rice varieties and root characteristics will also have a more obvious selective effect on the microbiomes with plant growth time.In contrast,lindane pollution has a relatively small impact,which may be related to the mitigating of lindane toxicity during rice growth in flooded soils.Correspondingly,the responses of root-associated microbiomes of rice to pollution stress under different conditions also feed back to the underground ecological environment,further causing the different dissipation rates of lindane by regulating the degrading bacteria and microorganisms which involved in the soil redox processes.Comparing with rice,the assembly of root-associated microbiomes of maize and soybean are more sensitive to lindane pollution,which may be due to the unconducive aerobic environment to lindane dissipation generated by the cultivation of dryland plants.Therefore,this study proposes that complex plant-soil-microbe interactions under pollution stress can induce different root-associated microbiomes,and cause the varying dissipation rates of lindane in rhizosphere soils;Comparing with dryland plants,maize and soybean,rice cultivation is more beneficial to the self-purification of farmland soils polluted by residual organochlorine pesticides.