Effects of phosphorus on chemical forms of Cd in plants of four spinach (Spinacia oleracea L.) cultivars differing in Cd accumulation

In order to clarify how cadmium (Cd) chemical forms in planta relate to the genotype difference in Cd accumulation of spinach (Spinacia oleracea L.), two low-Cd and two high-Cd cultivars were compared under a hydroponic experiment with two concentrations of Cd (8.98 or 44.71 mu mol Cd L-1). The concentrations of phosphorus in the hydroponic system were also adjusted to two levels (0.5 and 1.0 mmol L-1) to investigate the influence of phosphorus on the forms and accumulation of Cd in the tested cultivars. Average Cd concentrations in shoots were 8.50-10.06 mg kg(-1) for high-Cd cultivars and 6.11-6.64 mg kg(-1) for low-Cd cultivars a under lower Cd treatment and were as high as 24.41-31.35 mg kg(-1) and 19.65-25.76 mg kg(-1), respectively, under a higher treatment. Phosphorus significantly decreased Cd accumulation in the tested cultivars, and the effect had superiority over the cultivar alternation under higher Cd stress. Cadmium in the NaCl-extractable fraction of the plant tissues showed the greatest relationship to genotype difference of Cd accumulation. The difference in the capacity to binding Cd into F (HAc), F (HCl), or F (Residue) was another important mechanism involving in the genotype difference in Cd accumulation of spinach. Among them, average proportion of Cd in F (HAc) in low-Cd cultivars was higher than that in high-Cd cultivars in association with the effect of phosphorus.