Response of submerged plant (Vallisneria spinulosa) clones to lead stress in the heterogenous soil.

In order to evaluate risk spreading among clones and antioxidant defence response of clonal ramets, turions of Vallisneria spinulosa, the dominant clonal plant of the submerged plant community in most of the lakes in Middle and Lower Reaches of Yangtze Rive, China, were planted in the heterogeneous soils contaminated with 40 and 160 microg g(-1) Pb (dry weight) in a greenhouse. After 100 d, the ranking order of tissue Pb concentrations in organs of the ortets (parental plants) was root>turion>rhizome>leaf, but that of tissue Pb quantities was leaf>turion>rhizome>root, due to their different biomass. Some of Pb was transferred from the ortets exposed in the Pb-supplied soil to leaves of the offspring growing in the favorable patch through rhizome (connective organ). A high foliar Pb concentration induced a significant decrease in superoxide dismutases, peroxidase and catalase activities. Catalase was more sensitive to Pb than the other two antioxidant enzymes. However, a low foliar Pb concentration, in the ortets exposed to 40 microg g(-1) Pb and in all of the offspring, slightly increased the activities of superoxide dismutases and peroxidase. The biomass accumulation per ortet and the biomasses percentages allocation to the roots and the leaves in Pb treatments decreased markedly. Nevertheless, there was no significant difference in biomass accumulation of the offspring between the low Pb level treatment and the control. The biomass percentage allocated to the root of the offspring was found to be larger than that of the ortets.