Characteristics And Mechanisms Of Cadmium Uptake And Accumulation In Different Soybean Varieties

Heavy metals are becoming more serious soil pollutants world-wide,and that is especially true of cadmium.The toxic cadmium ion is a serious threat to humans when transferred through the food chain.Soybean is an oilseed crop with multiple uses and it is widely cultivated in many regions in China.Many studies have shown that the vegetative organs and seeds of soylbean are affected by the absorption and accumulation of cadmium(Cd2+).However,to our knowledge,there are few reports on the characteristics of cadmium absorption and accumulation by different types of soybeans.In this incubator study,four soybean varieties with different abilities to take up Cd2+were selected to grow in soils with different Cd2+ concentrations.By measuring the Cd2+ content in roots,stems,leaves,pods and seeds of soybean,the accumulation and translocation factor of cadmium in different soybean organs was calculated.The effect of Cd2+ enrichment on the growth of soybean is discussed in relation to the characteristics of Cd2+ uptake and accumulation in different soybean varieties.The main results of this paper are the following:1.Effects of Cd2+on the growth of different soybean varietiesThe 0.35 mg·L-1 Cd2+ treatment had no significant effect on the growth of different soybean varieties compared to the control(0 mg·L-1 Cd2+).Similarly,the 0.35 mg·L-1 Cd2+ treatment had no significant effect on dry matter accumulation,plant height,pod number,leaf area and yield per plant for any of the four different soybean varieties.However,leaf area under the 0.35 mg·L-1 Cd2+treatment was slightly higher than under the control.Analysis of variance showed that dry matter content differed among varieties under the same Cd2+ treatment.2.The uptake ability of Cd2+ in different organs of soybean varietiesThe results showed that the Cd2+ content in the organs of the four soybean varieties at R5 and R8 stages was significantly increased with Cd2+ content in the soil.There were big differences in the Cd2+ content of different organs at R5 and R8 stages.The Cd2+ contents in organs were:roots>leaves>stems>pods.The Cd2+ concentration in the roots of the low Cd2+ accumulating varieties was significantly higher than in the high accumulating varieties at the R5 and R8 stages.However,the Cd2+ content in the stems,leaves and pods of the high Cd2+ accumulating varieties was higher than in the low Cd2+ accumulating varieties.The Cd2+ uptake in low Cd2+ accumulating varieties'roots was less likely to be transferred,and Cd2+ concentration in roots was more stable compared to that in high Cd2+ accumulating varieties.Correlation analysis showed that Cd2+ content in stems,leaves,pods and seeds was positively correlated with Cd2+ concentration in the soil.The increase in Cd2+ content of stems,leaves and pods in all varieties promoted Cd2+ transfer to seeds at R5 and R8 stages.But there was no correlation between Cd2+ content in roots and Cd2+ content in seeds.The results showed that the percentage Cd2+ content was different in different organs at both R5 and R8 stages in all varieties.This was most evident in roots,where the proportion of Cd2+ content was largest,29.58%-70.40%of the total Cd2+ content.In addition,the proportion of Cd2+content in organs differed among varieties.The proportion of Cd2+ content in roots of low Cd2+accumulating varieties was significantly higher than in high Cd2+ accumulating varieties,while the proportion of Cd2+ content in stems,leaves and pods was higher in the high Cd2+ accumulating varieties.3.The Cd2+ enrichment coefficient and Cd2+ translocation factor of different soybean varietiesThe results showed that the Cd2+ enrichment coefficients differed among soybean varieties.The Cd2+ enrichment coefficients of four varieties were:H1>H2>N1>N2.The Cd2+ enrichment coefficients of stems,top leaves,bottom leaves and pods of high Cd2+ accumulating varieties were significantly higher than those of low Cd2+ accumulating varieties,while Cd2+ enrichment coefficients of roots of low Cd2+ accumulating varieties were higher than those of high Cd2+accumulating varieties.The Cd2+ enrichment coefficients at the R5 stage were:roots>bottom leaves>stems>pods>top leaves.The Cd2+ enrichment coefficients in roots were the highest,ranging from 0.19 to 0.64,The highest Cd2+ enrichment coefficient was in roots of the low Cd2+accumulating variety at the R8 stage,while the highest Cd2+ enrichment coefficient of high Cd2+accumulating varieties was in the leaves.The Cd2+ enrichment coefficients of high Cd2+accumulating varieties were significantly higher than those of low Cd2+ accumulating varieties in 2015 and 2016,123.53%and 127.59%higher,respectively.The results showed that there were differences in the Cd2+ translocation factor in different organs of soybean at the R5 stage.It is obvious that at R5 the Cd2+ translocation factors of the leaves were generally higher than those of other organs.The Cd2+translocation factors of stems,top leaves,bottom leaves,top pods and bottom pods of high Cd2+ accumulating varieties were significantly higher than in low Cd2+ accumulating varieties.The roots of high Cd2+ accumulating varieties transferred more Cd2+ to the organs above ground,while this was reversed for low Cd2+accumulating varieties.The Cd2+ translocation factor in leaves was also generally higher than for other organs at the R8 stage.The Cd2+ translocation factor in stems,leaves,pods and seeds of high Cd2+ accumulating varieties were higher than in low Cd2+ accumulating varieties.The ability to accumulate Cd2+ in roots of high Cd2+ accumulating varieties was lower than that in low Cd2+ accumulating varieties,but the Cd2+ transferred from roots to stems and leaves was higher in high Cd2+ accumulating varieties,which resulted in higher Cd2+ accumulation in above ground organs of high Cd2+ accumulating varieties than in low Cd2+ accumulating varieties.