Soil Arsenic Remediation Effect And Its Mechanisms For Intercropping Models Of Pteris Vittata L. And Crops

In recent years,a large number of heavy metals have entered the soil environment due to the rapid development of industry and agriculture.Arsenic?As?is listed as one of the ten dangerous chemicals by the World Health Organization,and the remediation of As-contaminated soils is urgently needed.Phytoremediation is an economic,efficient and sustainable way for arsenic control,and has high applicability in remediation of large-scale farmland pollution.Pteris vittata L.,an As hyper-accumulator with large above-ground biomass and a high As enrichment coefficient,has widely used in remediation of soil As pollution.However,the effects and mechanisms of P.vittata remediation modes are not well understood,which limits its application in practice.In this study,a set of intercropping modes of P.vittata and crops were studied per both field experiments and green house experiments to elucidate remediation effects asn well as the preliminary mechanisms including soil As fractionation,microbe diversity,root exudates,the As uptake kinetics.The main results are as follows:1. Field experiment was conducted to study the effects of different intercropping modes with P.vittata and corn on As remediation.The results showed that,in the first year,the content of As in the corn grains of all intercropping modes?T1,T2,T3,T4,T5?was lower than 0.5 mg/kg,significantly lower than that of corn monoculture?CK1?,with a decrease of 35.4%?59.8%;in the second year,no As was detected in corn grains of all treatments,and the extraction amount of soil As by the 5 intercropping modes was 13.47?62.80 g/mu,of which T5 mode?equal 4 row spacing corn with equal 4 row spacing P.vittata?had the highest remediation efficiency.2. The effects of intercropping on corn yield and economic benefits were studied per field experiment.The results showed that compared with CK1,all intercropping modes did not decrease the corn yield significantly due to the increase of 100-kernel weight by10.0%?16.6%.The economic benefit analysis of corn showed that the net benefit of T2mode?wide narrow row corn with double row P.vittata?reached 719.3 yuan/mu,which was 11.9%higher than that of CK1 mode;However,intercropping with P.vittata increased the input,and resuled in decrease of benefit cost ratios of each mode by 17.4%?41.2%,among which T1 mode?wide narrow row corn with single row P.vittata?had the smallest decline.3. Soil As in different intercropping modes were fractionationed and the results showed that,as compared with soils without crops,the percentage of Fe-bound As for intercropping modes decreased by 2.0%?8.6%,but increased by 2.3%for corn monoculture mode?CK1?.Intercropping increased the proportion of Ca-bound As by1.4%?4.9%,which was significantly higher than that of corn monoculture mode?CK1?by 0.2%,indicating that intercropping promoted the transformation of Fe-bound As into Ca-bound As.There was no exchangeable As in the soil tested,and there was no significant change in Al-bound As and residual As,accounting for 0.0%?3.9%and54.0%?64.1%of total arsenic in soils,respectively.4. The antioxidant responses of corn and P.vittata under different intercropping modes were studied under field condtions.The results showed that CAT activity of 5intercropping modes?T1,T2,T3,T4,T5?was increased by 34.1%?158.5%compared with CK2 mode?P.vittata monoculture?,among which T4 mode?equal row spacing corn with double row P.vittata?increased the most;GSH content of P.vittata leaves in intercropping modes were higher than CK2 mode?104.2%?793.6%?,and T2 mode?wide narrow row corn with double row P.vittata?increased the most.5. Analysis of soil microbial diversity for different intercropping modes showed that the most abundant bacterial communities were Acidobacteria,Proteobacteria and Chlorflexa.Compared with corn monoculture,the diversity of soil microorganism increased significantly after intercropping.Meanwhile,the abundance of Acidobacteria and Chlorflexa for intercropping modes decreased significantly,while that of Proteobacteria increased.6. The effects of P.vittata,corn,Ricinus communis L.and their intercropping systems on root exudates under As stress were studied.The results showed that,under 5 mg/L As stress,compared with C treatment?corn monoculture?,PC treatment?P.vittata with corn?increased oxalate by 21.3 times,tartaric by 16.6 times,and succinic appeared,and the content was 1.03 mg/g.Compared with R treatment?R.communis monoculture?,PR treatment?R.communis with P.vittata?increased oxalate by 57.2%,and succinic appeared,the content was 0.46 mg/g.7. The kinetics of As uptake by P.vittata,corn,R.communis and their intercropping modes was studied under hydroponic conditons.The results showed that C_min and K_m of As???in all treatments decreased by 5.5%?37.9%and 9.0%?31.7%compared with As???,and V_max of all treatments except PR treatment?P.vittata with R.communis L.?increased by 39.1%?374.6%compared with As???.These results showed that all treatments had higher affinity for As???uptake.8. Comparation of As absorption kinetics for different intercropping modes showed that,compared with C?corn monoculture?,PC treatment?P.vittata with corn?increased C_minby 12.9%to 43.8%,K_m by 8.4%to 27.8%,decreased V_max by 38.1%to 85.0%.Compared with R?R.communis monoculture?,PR treatment?P.vittata with R.communis?increased C_min by 141.5%to 267.6%,K_m by 66.3%to 121.6%,decreased V_max by 19.8%to 53.8%.These indicated that the affinity of the two intercropping modes?PC,PR?for As??,??absorption decreased significantly compared with their single modes?C,R?.9. The effect of the intercropping modes of P.vittata and corn on the uptake of P and As was studied by hydroponics.The results showed that,in high P?>30 mg/L?concentrations,addition of P significantly inhibited the absorption of As by corn and P.vittata;low concentrations of As?0-1.8 mg/L?did not affect the uptake of corn P,but high concentrations of As?>1.8 mg/L?significantly inhibited the uptake of corn P;in low P?1mg/L?concentration,the addition of P and As significantly promoted the uptake of P and As by P.vittata.