CHEMICAL FRACTIONS AND PHYTOAVAILABILITY OF COPPER TO RAPE GROWN IN THE POLLUTED PADDY SOIL

This paper focuses on the phytoaccumulation and translocation of copper (Cu) in rape grown in the Cu-polluted paddy soil. Pot experiments were conducted in greenhouse conditions to examine the Cu availability and uptake by rape in a paddy soil. The soil was spiked with different concentrations of Cu (0, 100, 300, 500 and 1,000 mg kg−1 soil, added as CuSO4) to simulate soil Cu contamination. After 8 months of growth, plant shoots, stems, pod shells and rapeseeds were harvested for analysis. The concentrations of Cu in the roots and aerial parts of the rape and available Cu in soils were then extracted and determined. Chemical fractions of Cu in the paddy soil of rape were also investigated by sequential extraction techniques. The findings showed that Cu in the clean paddy soil was mainly distributed in residual fractions. However, the most drastic increase was observed in Fe–Mn oxides-bound fractions and organic-bound fractions with increasing soil Cu concentrations. Exchangeable fractions played a more important role than other fractions in controlling the mobility and phytoavailability of Cu. Rape growth was stimulated by low concentrations of Cu, but inhibited by high concentrations. Compares to the aerial parts, the roots were more sensitive to Cu toxicity. The correlation analysis showed that Cu in exchangeable fractions made the greatest contribution on the accumulation of Cu in rapes. The factor analysis results showed that the exchangeable fractions in roots can be indicator of Cu availability. Meanwhile, the bio-concentration factors and the translocation factors of Cu in rape were determined and the results showed that Cu had lower accumulation in the edible parts of the rape.