Growth responses, antioxidant enzyme activities and lead accumulation of Sophora japonica and Platycladus orientalis seedlings under Pb and water stress

The effects of lead were investigated in forest trees (Sophora japonica and Platycladus orientalis) grown in soil and exposed to Pb(CH3COO)2·3H2O (0, 300, 500, 1,000 mg kg−1) with different levels of water stress (100, 80, 60, 40 % soil relative water content, SRW). The results showed that, in the presence of Pb, the ground diameter, height and dry weight were greater than the control for S. japonica and P. orientalis. The proportions of biomass allocation of S. japonica were root > stem > leaf, and of P. orientalis leaf > stem > root except for 40 % SRW. SOD (superoxide dismutase) and POD (peroxidase) activities in leaves were activated by soil Pb for P. orientalis, while SOD activities increased but POD activities decreased compared with control under Pb stress for S. japonica. Water stress increased SOD and POD activities under different Pb concentrations, also increased MDA (malondialdehyde) content significantly. For S. japonica, the Pb concentration in the root was up to 91.9 mg kg−1, while the Pb concentration in the aboveground part was 37.5 mg kg−1. The Translocation Factor (TF value) increased with the increase of water stress intensity, under the same Pb concentration. For P. orientalis, the Pb accumulation in the roots was significantly higher than that in the aboveground part (TF < 1.0). And the total amount of Pb accumulated in P. orientalis was higher than S. japonica. On the basis of this study, it could be concluded that P. orientalis was more suitable for usage in the mining areas of northwest China to accumulate heavy metals, compared with S. japonica.