[Conformation transformation of lead in rhizosphere]

With rhizoboxes, this study dealt with the distribution and conformation transformation of lead in the rhizosphere and non-rhizosphere of wheat and rice grown on red soil. The results showed that the predominant forms of lead were acid dissolved and Carb-Pb (bound to carbonates), Exch-Pb (exchangeable-Pb), and FeMnO-Pb (boud to iron and manganese oxides). Exch-Pb in the rhizosphere of both rice and wheat was much higher than those in the non-rhizosphere, which means that the activation process in the rhizosphere was very strong, and bio-available Pb greatly increased. Various levels of Pb treatment and Pb-Cd interaction also had certain effects on the distribution of lead. In treatment of low Pb concentration, FeMnO-Pb was higher than Exch-Pb, but the contrary result was observed in treatment of high Pb concentration. Both Exch-Pb and FeMnO-Pb in wheat rhizosphere decreased with an increase of Cd. Exch-Pb in rice rhizosphere was correlative to the Cd content in soil. Compared with the treatment in the absence of Cd, the activation of Exch-Pb in rice rhizosphere was weaker in 5 mg Cd.kg-1 treatment, but stronger in 10 mg Cd.kg-1 treatment.