Effects of citric acid and EDTA on the absorption and translocation of Pb and nutrient elements in Coleus blumei

To investigate the effects of citric acid and EDTA-Na2 on growth and characteristics of absorption and transportation of Pb and six essential nutrient elements (N, P, K, Ca, Mg, and Fe) of Coleus blumei exposed to Pb pollution, an experiment was conducted with eight treatments, including the control, 6 mmol·L-1 Pb pollution, and 6 mmol·L-1 Pb pollution mixed with 1, 5, or 10 mmol·L-1 citric acid or 1, 5, or 10 mmol·L-1 EDTA-Na2 on potted C. blumei plants. Compared with that in the control, Pb pollution caused a decrease in dry weight, water content, and root dehydrogenase activity. Except for N content in roots, and Ca content in leaves and roots, the contents of other nutrient elements were lower in plants exposed to Pb than in the control, whereas the accumulation amount of Pb increased. In contrast, under other conditions, such as the treatments of Pb pollution mixed with the addition of 1, 5, or 10 mmol·L-1 citric acid or 1, 5, or 10 mmol·L-1 EDTA-Na2, significant decreases in dry weight, water content, and root dehydrogenase activity were observed. Changes in Pb content, the accumulated amount of Pb, and content of six nutrient elements varied with different treatments. C. blumei accumulated more Pb in shoots (leaf and stem) under the lower concentration treatment (1 mmol·L-1) of citric acid than EDTA-Na2, but the higher concentration treatment of (5 and 10 mmol·L-1) citric acid showed the opposite trend. Therefore, it was concluded that the suitable concentration of citric acid or EDTA-Na2 could enhance the Pb absorption ability of C. blumei.