The Function And Mechanism Of Seed Endophyte H5 On Enhancing Dysphania Ambrosioides Heavy Metal Resistance

Soil heavy metal(HM)contamination has become to be a severe environmental problem worldwide.Microbe-assisted phytoremediation was considered as one of the most promising technologies due to its low cost and environment friendly nature.Dysphania ambrosioides L.is a dominant plant in HM-contaminated mining areas of Huize county,Yunnan Province,China.It exhibits excellent adaption to HM-contaminated environments,suggesting a potential use in phytoremediation of HM-contaminated sites.In the study,the functional properties of 9 seed endophytes of D.ambrosioides were tested.The functional properties included nitrogen fixation,phosphorus and potassium solubilizing,heat and cadmium resistance as well as seed germination promotion ability.Further,the role of H5(Bacillus subtilis),which showed better phosphorus solubilization,etc.,were evaluated by series of pot experiments.The main contents and results of the study are as follows:1.The result showed that some seed endophytes of D.ambrosioides had the ability of nitrogen fixation,phosphorus and potassium solubilization,and high-temperature and cadmium resistance.Among them,H5 showed the best performance,and its phosphorus solubilization arrived 78.75 mg/L.Its growth rate was 1.02 cm/d at 50℃and the minimum inhibitory concentration of cadmium was 300 mg/L.2.The seed germination promoting test on plates showed that the inoculation of H5 significantly improved the seed germination rate at 30 and 50mg/L cadmium stress,and at 50 mg/L,the germination promotion effect was the better,reached 90%.Similarly,the germination test on pristine soils collected from the mining area(cadmium concentration was 8.89 mg/kg)demonstrated that the inoculation of H5(E+)significantly increased the seed germination rate from63.6% to 80%(P<0.01,t-test)when compared with the control(mock-inoculated with H5),in addition,the germination time was shortened.3.The pot experiment showed that the plant height of E+ under 0 mg/kg cadmium stress,and the root length and dry weight of aboveground parts under15 mg/kg cadmium stress,as well as the root length,dry biomass of both aboveground and belowground parts under 30 mg/kg cadmium stress,all increased when compared with the control group.However,the difference was not significant(P>0.05,t-test);In addition,the inoculation of H5 increased the chlorophyll content of the host plants under 15 mg/kg cadmium stress,but the difference was also not significant(P>0.05,t-test).In terms of ability to fix nitrogen,solubilize phosphorus and potassium,and withstand high temperatures and cadmium,seed endophyte H5 was the best one.Moreover,H5 can significantly promote the germination of D.ambrosioides seed under heavy metal stress.Thus,H5 had a potential use in microbe-assistant phytoremediation of HM-contaminated sites.