Alleviation effects of calcium and potassium on cadmium rhizotoxicity and absorption by soybean and wheat roots

The objectives of the present study were to investigate the root responses of soybean (Glycine max L.) and wheat (Triticum aestivum L.) seedlings to cadmium (Cd) stress and to investigate the alleviation effects of Ca and K on rhizotoxicity and absorption of Cd by roots. Soybean and wheat seedlings in a hydroponic system were exposed to Cd-spiked solutions (0, 4, 8, 12, and 16 M) with different Ca (0.5, 1, and 10 mM) and K (0.3, 1.2, and 9.6 mM) levels for 7 d. The results showed a dramatic reduction in root elongation of soybean due to increased Cd, but increasing Ca and K levels alleviated this reduction in soybean. The amelioration of Cd toxicity by the addition of Ca may be associated with reduced Cd absorption. However, the addition of K in reducing Cd toxicity might not be dependent upon Cd absorption. Compared with soybean, wheat showed a relatively high tolerance to Cd. The alleviation of Cd rhizotoxicity in wheat was more apparent by K than by Ca. We found that the addition of K promoted root elongation but not directly prevent Cd stress, and that the addition of Ca minimized acute rhizotoxicity of Cd in wheat. Moreover, the addition of Ca reduced Cd absorption by soybean and wheat roots. However, the addition of K only reduced Cd absorption by wheat roots.