The Alleviation Of Heavy Metal Toxicity In Alfalfa-rhizobia Symbiotic System By Signalling Molecule

Soil heavy metal pollution is a universal environment problem across the word.Legume combined with rhizobium to restore polluted soil by heavy metal is widely used,but symbiosis of them is restrained.In the symbiosis of legume and rhizobium,many physiological processes are regulated by hydrogen sulfide and nitric oxide.Currently,the research to study the relief of hydrogen sulfide and nitric oxide to the stress of the plants is mostly conducted in the method of hydroponics,and little is done in the conditions of original polluted soil.In another way,in the symbiosis of legume and rhizobium,the regulation of hydrogen sulfide and nitric oxide is not yet figured out.Consequently,the symbiosis of medicago sativa and Sinorhizobium meliloti CCNWSX0020 with hydrogen sulfide and nixtric oxide is selected for this research to explore the regulation of these two signaling molecules to the symbiosis and the change of soil microbial community.It's concluded as following:1.Combined application of hydrogen sulfide and S.meliloti or nitric oxide and S.meliloti both can add the biomass on the ground and underground.Combined application of hydrogen and S.meliloti makes the dry weight of medicago sativa above ground increase by 9.6% and the dry weight of medicago sativa underground increase by 16.1%.Combined application of nitric oxide and S.meliloti makes the dry weight of medicago sativa above ground increase by 11.0% and dry weight of medicago sativa underground increase by 22.3%.2.Combined application of hydrogen sulfide and S.meliloti or nitric oxide and S.meliloti can both reduce the the absorption of heavy metal by the plants.Combined application of hydrogen sulfide and S.meliloti makes the absorbed Pb reduced by 24.3% and 22.5% respectively for the above ground and underground part of medicago sativa;the absorbed Cd is reduced by 16.1% and 35.1% respectively for the above ground and underground part of medicago sativa.Combined application of nitric oxide and S.meliloti makes the absorbed Pb reduced by 43.43% and 43.64% respectively for the above ground and underground part of medicago sativa;the absorbed Cd is reduced by 12.65% and 36.1% respectively for the above ground and underground part of medicago sativa.In addition,combined application of two signaling molecules with S.meliloti makes the Pb and Cd absorption reduced to the lowest level for the underground part of the plants compared with the other treatments.3.Combined application of these two signaling molecules with S.meliloti can improve the activity of the SOD/POD/APX/CAT antioxidase in the plants and reduced the content of ROS and MDA,thus to strengthen the oxidation resistance of the plant,and increase the heavey metal tolerance of the plant.4.Combined application of hydrogen sulfide and S.meliloti or nitric oxide and S.meliloti produces different influence to the edaphon.In the combined application of these two signaling molecules and S.meliloti,the superior spescies in the level of soil bacteriophyt are Proteobacteria?Actinobacteria?Acidobacteria and Firmicutes.In the level of bacteria genus,combined application of hydrogen sulfide and S.meliloti increses not only the abundance of endogenesis bacteria,Nocardioides and Glycomyces at plant plant root,but also the abundance of Bacillus transformed by P.But combined application of nitric oxide and S.meliloti will restrain the growing of endogenesis bacteria,Nocardioides,Glycomyces and Ensifer at plant plant root.The combined application of these two signaling molecules and S.meliloti has no influence on the soil bacteria community.