Physiological Basis Of Apple’s Accumulation And Tolerance To Heavy Metal Cadmium Under Different Soil Conditions

Heavy metal cadmium(Cd)pollution in agricultural soil is becoming more and more prominent due to the unreasonable use of pesticides and fertilizers,sewage irrigation,and unreasonable discharge of industrial and automobile exhaust gas.Cd pollution in soil affects the healthy and sustainable development of apple industry.Cd is a non-essential element for plant growth.It has high migration ability and will be transported and accumulated in plants after being absorbed.It will not only affect the growth and development of crops,but also pose a serious threat to human health through the food chain.Physical and chemical properties of soil can affect the bioavailability of Cd in soil,thus affecting the absorption,translocation,accumulation and tolerance of Cd by plants.The soil in this experiment was taken from Hanfu apple orchards in five areas: Maliangou Village,Xidayao Town,Liaoyang City(A);Desheng Village,Desheng Town,Panjin City(B);Xishan Village,Beisijiazi Town,Chaoyang City(C);Kaoshantun Village,Xinnongcun Town,Xinmin City(D);and Qianertaizi Village,Liangshan Town,Xinmin City(E).Grafted seedlings were planted in 5 kinds of soil and treated with 0 or 500 μM Cd for 70 days.The effects of different soil physical and chemical properties on Cd uptake,transport and accumulation of grafted seedlings were discussed from physiological and molecular levels.The main results are as follows:1.Soil organic matter content,cation exchange capacity,silt content and sand content were the main factors affecting Cd uptake by seedlings.The soil available Cd content had a very significant negative correlation with cation exchange capacity,but a very significant positive correlation with sand content.The content of acid soluble Cd was significantly positively correlated with the root and stem Cd content of seedlings.2.Under Cd treatment,compared with the other three soils,the lower organic matter content,cation exchange capacity,silt content and higher sand content in soils B and D resulted in higher available Cd content in soils,which further led to higher Cd accumulation in seedlings planted in these two soils.3.Cd treatment inhibited the biomass,chlorophyll content and root configuration parameters of most seedlings,and increased ROS and MDA contents in various tissues.Compared with the other three soils,the growth-related parameters of apple seedlings planted in B and D soil were inhibited more severely.The plants planted in these two soils had higher level of reactive oxygen species and suffered more Cd toxicity.Moreover,the non-enzymaticantioxidant content and antioxidant enzyme activity of seedlings planted in B and D soils were low,indicating that seedlings planted in B and D soils had poor tolerance to Cd toxicity.4.Compared with other soils,under Cd stress,the expression levels of genes related to Cd absorption and transport such as HA11,VHA4,IRT1,ZIP6,CS1,FRD3,HMA4 and PCR2 in the roots of seedlings planted in soils B and D were higher,while the transcription levels of genes related to Cd detoxification such as MHX,MTP1,ABCC1,MT2 and NAS1 were lower.Seedlings planted on other soils are the opposite.