Studies On The Photosynthesis,Cd Tolerance,Enrichment And Translocation Of Betula Platyphylla Suk.by Exogenously Inducing Under Cd Stress

Phytoremediation technology is an environmentally friendly technology for the treatment of soil heavy metal pollution.Selecting suitable plant samples,based on exogenous strengthening measures,inducing plant tolerance to soil heavy metal stress which is key research issues in the application of remediation technology.The woody plant named Betula Platyphylla Suk.,which has a large biomass and a developed root system,and has good environmental adaptability to soil stress and strong environmental adaptability.At present,the research mainly focuses on salt stress,drought stress and high temperature stress,and there are few reports on cadmium(Cd)stress.In this paper,birch is used as the research object.Based on chlorophyll fluorescence technology,the effects of exogenous ethylenediaminetetraacetic acid(EDTA),salicylic acid(SA)and proline(Pro)on the photosynthetic gas exchange parameters and chlorophyll fluorescence characteristics of birch seedling leaves were discussed;the effects of exogenous SA and Pro on Cd stress and the enrichment and transfer of Cd by birch,which provide detailed reference for tree species selection of Cd polluted soil remediation research.The main results are as follows:(1)Under 50 mg/kg Cd treatment,after 5-week stress,the Pn of birch increased by 11.84%compared with control,indicating that birch showed an excitatory effect on low-concentration Cd treatment.The parameters of ?PS?,qP,NPQ,and ETR of the birch leaves were maintained within a certain range under the treatment of less than 100 mg/kg Cd.The heat dissipation capacity of birch was partially ineffective under 200 mg/kg Cd treatment.Chlorophyll fluorescence parameters(Fv/Fm,?PS?,ETR and NPQ)of the birch showed a significant correlation trend with Pn and biomass(|r|>0.95,P<0.01),which proved that chlorophyll fluorescence technology can well characterize the intensity of photosynthesis of birch leaves.(2)Low concentration EDTA treatment(1?3 mmol/kg)significantly increased chlorophyll content,photosynthesis intensity,chlorophyll fluorescence intensity and biomass of birch,and significantly reduced membrane lipid peroxidation level(P<0.05).When the concentration of Cd pollution treatment is not greater than 100 mg/kg,EDTA with a concentration of 1 mmol/kg has the best effect.This showed that low concentration EDTA treatment could effectively alleviate the effects and damages of Cd stress on birch.Under the low concentration EDTA treatment,the birch's ability to enrich and transport Cd,including bioconcentration factor(BCF),transport factor(TF),accumulation(AC)and heavy metal extraction rate(MER),increased significantly,of which 100 mg/kg Under Cd treatment,1 mmol/kg EDTA treatment made the birch's MER reach 0.98%,accounting for 1.96 times of 100 mg/kg Cd treatment alone;under 200 mg/kg Cd treatment,2 mmol/kg exogenous EDTA treatment made birch MER reached 0.68%,accounting for 2.35 times of 200 mg/kg Cd alone.This indicated that EDTA treatment effectively improved the ability of birch to accumulate,transport and accumulate Cd,and further strengthened the ability of birch to repair Cd-stressed soil.(3)Spraying with SA and Pro significantly increased The biomass,chlorophyll content,and photosynthesis intensity of the birch(P<0.05),significantly reduce the level of membrane lipid peroxidation,and significantly reduce the AC and MER of birch to Cd.When sprayed at a concentration of 5 mmol/L,SA and Pro increased the TFroot-shoot of white birch by 2.86%and 5.71%compared to 100 mg/kg Cd alone.When sprayed with 5 mmol/L of SA,white birch TFshoot-leaf increased by 32.25%compared with 100 mg/kg Cd.When sprayed with 10 mmol/L of Pro,the TFshoot-leaf of white birch increased by 30.1 1%compared with 100 mg/kg Cd.This shows that the application of exogenous SA/Pro enhanced the transfer of Cd to the aboveground part of birch,reduced the oxidative damage of Cd to birch,promoted the synthesis of chlorophyll,and enhanced the resistance of birch.The research results showed that EDTA is better than SA/Pro in repairing birch.In phytoremediation,exogenous EDTA could effectively increase the accumulation and accumulation of birch to Cd,while spraying SA and Pro would reduce the accumulation,thereby promoting the healthy growth of birch.In terms of improving the resistance of white birch,exogenous EDTA treatment and spraying with SA/Pro treatment could effectively enhance the efficiency of light energy conversion,increase chlorophyll content,and alleviate the effect and inhibition of Cd on the activity of PS ? reaction center of birch leaves,thereby improving the resistance of white birch.