Cadmium And Lead Accumulation And Physiological Response Of Amaranthus Tricolor L.under Heavy Metal Stress From Soil And Atmosphere

Heavy metal pollution has become a serious environmental problem.A large amount of heavy metal in cultivated land in China exceeds the standard,of which Cd and Pb are seriously polluted.Heavy metals are highly mobile in the soil-plant system,making soil an important source of heavy metals in plants.In addition,atmospheric deposition can also increase the accumulation of heavy metals in plants.Most of the current research on the impact of heavy metals on plants is based on the single pollution of the environment by soil or atmosphere.Realistic conditions,such as coal-fired power plants,mining,smelting,transportation emissions and other pollution sources,crops are often subject to double pollution stress from heavy metals in the soil and atmospheric deposition,but their cumulative distribution and physiological response of heavy metals have not been paid enough attention,which is not conducive to the comprehensive prevention and control of regional heavy metal pollution and Crop safety.In this study,Amaranthus tricolor L.was used as the research object.Cd,Pb solution spraying and Cd,Pb contaminated soil pot experiments were conducted to investigate the influence of Cd,Pb from atmospheric deposition and soil on the growth,cumulative,chemical morphology,physiological and biochemical responses of amaranth seedlings and mature plants.Research indicates:（1）Soil is the main source of Cd（92-98%）and Pb（68-94%）in amaranth,and it accumulates in the roots in large quantities.Atmospheric deposition can also effectively increase the content of Cd（2-3%）and Pb（18-28%）in stems and leaves.Most of Cd and Pb in amaranth cells are stored in the cell wall,but they will be transferred into vacuoles under high concentration of soil stress.Cd in amaranth is mainly combined with pectin and protein,Pb is mainly insoluble phosphate and oxalate,and the low active chemical form accounts for a large proportion,which is conducive to improving the tolerance of amaranth to heavy metals.Cd in two heavy metals has higher mobility and biotoxicity.The absorption and distribution of Cd and Pb by amaranth was related to the stress concentration and pathway of heavy metals.（2）Atmospheric stress alone mainly promoted the growth and development of amaranth,and the growth parameters such as plant height and fresh weight reached the maximum in the HA group.High-concentration soil stress alone and soil atmospheric co-stress inhibited the growth of amaranth,and most of the growth parameters reached the minimum in the HSHA group.Due to the short exposure period,amaranth seedlings showed better tolerance compared to mature plants.（3）Cd and Pb in atmospheric deposition promote the growth and development of amaranth and the synthesis of soluble sugars and proteins in leaves,but Cd and Pb in high-concentration soils are inhibitory,mainly manifested by hydrogen peroxide（H₂O₂）and malondialdehyde（MDA）content increased,causing severe damage to the cell membrane.When the content of Cd and Pb in amaranth is low,the increase of antioxidant enzyme（Peroxidase（POD）,catalase（CAT）,superoxide dismutase（SOD））activity and antioxidant（Ascorbic acid（As A）,glutathione（GSH））content can effectively alleviate the oxidative stress caused by heavy metals,but when the content of Cd and Pb is too high,it will fail and damage the plant cell antioxidant system.Therefore,the accumulation and physiological response of plants to Cd and Pb under multi-source pollution stress are mainly affected by the soil heavy metal concentration.Although the effect of atmospheric deposition is small,it cannot be ignored.These findings would provide an important theoretical basis for risk assessment and pollution prevention of vegetables in areas with multiple sources of heavy metal pollution.