Effect Of Extracellular Products Of Roots Of Suaeda Heteroptera On Cd Removal By Bacteria

Heavy metals belong to a class of pollutants which are difficult to degrade in natural environment,and they are enriched.The excessive concentration of heavy metals in soil can cause toxicity to plants,affect the absorption and transportation of trace elements,and then affect their growth.Through the food chain,it threatens human health.At present,the pollution of heavy metals to the environment has become a worldwide concern.Panjin Red Beach is a beach wetland that has been listed in the list of international important wetlands.It is also an important eco-tourism resource in China.The pioneer plant Suaeda heteroptera and its root microorganisms play a role in reducing metals.Taking Suaeda heteroptera,Microbacterium sp.?No.S1?and Pseudomom putida?No.Y3?as experimental objects,the growth of bacteria under the action of root exudates of Suaeda heteroptera,and the removal of cadmium by bacteria and Suaeda heteroptera under different concentrations of Cd stress were determined by hydroponic experiments.The bacterial content and Cd concentration in soil contaminated by metal Cd were studied.The removal efficiency of heavy metal Cd by Suaeda heteroptera combined with S1 and Y3 bacteria was studied.Result as follows:1.Composition and proportion of root exudates of Suaeda heteroptera:Alkanes,aromatic hydrocarbons,alcohols and organic acids are the main components of root exudates of Suaeda heteroptera.Organic acid components contain oxalic acid,malic acid acetate,lactic acid and amino acid,which account for 97%of the total organic acid.There are 18 main amino acids,among which glycine secretion is the largest,accounting for 11.82%of the total,and cystine is the least,accounting for only 0.97%of the total.2.Effects of root exudates of Suaeda heteroptera on S1 and Y3 bacteria:Hydroponics experiments showed that Microbacterium sp.?No.S1?and Pseudomom putida?No.Y3?with Suaeda heteroptera could coexist in an environment,and could normally grow and release root exudates.In the absence of Cd stress,after 14 days of hydroponic culture,the bacterial content of the experimental group containing only S1 bacteria was 3.6×10⁶ cfu/mL,that of Suaeda heteroptera+S1 was 9.8×10⁶ cfu/mL,that of the experimental group containing only Y3 bacteria was 3.0×10⁶cfu/mL,and that of Suaeda heteroptera+Y3 was 3.7×10⁶ cfu/mL.The root exudates could promote the growth of S1 and Y3 bacteria.3.The degradation of Cd by root exudates of Suaeda heteroptera combined with S1 and Y3 bacteria at different concentrations:Under the stress of 0.2 mg/L Cd²⁺,root exudates of Suaeda heteroptera had a better promoting effect on the growth of Y3 bacteria,and the degradation rate of Cd by Suaeda heteroptera combined with Y3 bacteria was higher.Under the stress of 1.0 mg/L Cd²⁺,root exudates of Suaeda heteroptera could promote the growth of S1 bacteria better,and the combined effect of Suaeda heteroptera and S1 bacteria had higher degradation rate of Cd.Under Cd stress of different concentrations,the chlorophyll content of Suaeda heteroptera+Y3 experimental group was the highest.Y3 bacteria could better promote the growth of Suaeda heteroptera and release more root exudates. The above results also prove the feasibility of the combination of Suaeda Heteroptera and S1 and Y3 bacteria in remediation of heavy metal contaminated soil.4.Soil experiments showed that with the continuous growth of Suaeda heteroptera, the growth of two bacteria was promoted.The interaction between Suaeda heteroptera and two bacteria could enhance the removal ability of high concentration Cd contaminated soil.