The Effect And Mechanism Of Intercropping On Heavy Metal Absorption Of Pepper And Maize

Agricultural production had been seriously threated by the heavy metal because of its accumulation. The heavy metals affected not only the crops yield and quality, but also the health of the people for the bioaccumulation of the food chain. Intercropping is one of the most important planting methods in China. To a certain extent, interaction of crop root exudates can affect the soil pH value, enzyme activity, microbial population structure, heavy metal activity, etc. That of indicators of soil quality directly affected the crops growth, physiology and biomass, and affected the absorption characteristics of heavy metals in crops. In this study, pepper were used as the target, Cd and Pb were used as the model pollutants, which is not need in agricultural soil. By simulation experiment of intercropping of pepper and maize by root box to explore the effect and mechanism of interspecific interaction on the absorption of heavy metals in pepper, in order to find a more effective way to reduce the heavy metal content in the soil, and to achieve the safe consumption of pepper and other vegetables.In this study, the pepper were used as the research object, maize were used as interaction crop. 5 pollution levels by Cd(0、0.5、1、4、16 mg·kg-1)and Pb(0、50、100、400、1600 mg·kg-1)were set respectively. The experimental results were as follows:(1) Under the stress of Cd and Pb, the heavy metal content in different parts of pepper that intercropping with maize were lower than that of monoculture pepper. In Cd(0.5~16 mg·kg-1)contaminated soil, the exchangeable and carbonate bound states of Cd in the intercropping and non intercropping soil were 0.12~3.82 mg·kg-1and0.10~3.15 mg·kg-1 respectively; In Pb(50~1600 mg·kg-1) contaminated soil, the exchangeable and carbonate bound states of Pb in the intercropping and non intercropping soil were 4.91~123.49 mg·kg-1and 4.83~121.06 mg·kg-1respectively. But residue state, the content of Cd and Pb in the intercropping pepper soil was lower than that in non intercropping. The content of Cd and Pb was lower in each part of theintercropped pepper than that of the non intercropped pepper. But the exchangeable and carbonate bound states of Cd, Pb were greater than that of in non intercropping.(2) With the increase of Cd and Pb content, the plant height, stem diameter, leaf number and dry weight of the pepper were decreased, and the degree of reduction was positively correlated with the heavy metals concentration. The toxic effects of heavy metals were relieved with pepper and maize intercropping. The pepper root weight increased 3.59 %~5.82 %, pepper stem weight increased 3.03 %~18.59 %, pepper leaves weight increased 0.34 %~17.93 %, biomass index of single pepper weight and yield per plant were also increased.(3) Cd and Pb inhibited the net photosynthetic rate, stomatal conductance,intercellular CO2 concentration, transpiration rate, chlorophyll a and chlorophyll b.When the content of Cd was 16 mg·kg-1, Pb was 1600 mg·kg-1, the inhibition was the largest, and which was significantly different with low Cd, Pb concentration. The intercropping of pepper with maize alleviated the heavy metal inhibition effect on the photosynthetic index of pepper, and the index of photosynthesis was increased.(4) Heavy metal Cd and Pb also showed inhibitory effect on the activity of H2O2 ferment and acid phosphatase in soil, moreover, the inhibition of Cd on H2O2 ferment and acid phosphatase activity was stronger than Pb, and the activity of H2O2 ferment and acid phosphatase was increased by intercropping of pepper and maize.(5) We can see from the metagenomic 16 sDNA sequencing results, intercropping treatment had more bacterial flora than that of intercropping. And the number of bacteria flora in the soil treated by Cd was higher than the treatments that had no Cd. By groping, explain that the heavy metals affected the composition of the rhizosphere microorganisms.