Sex-specific responses to Pb stress in Populus deltoides: root architecture and Pb translocation

Pb-induced negative effects on Populus deltoides root growth were sex-related and branch-order specific. Pb translocation from lower- to higher-order roots was correlated closely with the structural heterogeneity in fine-root architecture. Growing evidence has revealed sexual dimorphism in the aboveground processes of poplars under environmental stresses. However, the belowground performance of poplars has not been well studied to date. Moreover, both structure and function differ markedly among different fine-root orders. Nevertheless, little information is available concerning root branch-specific responses to environmental stresses. In this study, Populus deltoides was employed as a model species to detect sexual differences in root morphology, architecture and metal accumulation under Pb stress. Compared with plants in control conditions, Pb decreased total root length, total surface area, root diameter and biomass, but markedly increased the Pb concentration and accumulation in both sexes. In general, Pb-induced changes in the measured parameters were greater in females than these in males. In contrast to changes resulting from the Pb concentration, root Pb storage was lowest in middle-order roots. Compared to higher root orders, Pb often caused more significant effects on root length, surface area and Pb concentration in lower orders, except for root diameter. The results demonstrate that females are more sensitive to Pb stress than males. In conclusion, males of P. deltoides could concentrate Pb in the roots of lower orders, and suppress transportation of Pb to high order of root. Moreover, negative effects of Pb were generally branch-order specific and Pb translocation was correlated closely with structural heterogeneity in fine-root architecture.