Sex-specific competition differently regulates ecophysiological responses and phytoremediation of Populus cathayana under Pb stress

Lead (Pb) contamination seriously threatens agroforestry production and safety. We aim to determine the interactive influence of Pb and sexual competition on the growth performance, photosynthetic and biochemical traits, ultrastructure and phytoremediation-related parameters of males and females. In the present study, eco-physiological responses and phytoremediation traits of Populus cathayana females and males were evaluated under interactive treatments of Pb and competition. There were significant sex-specific competition effects on biomass partition, photosynthetic activities, carbohydrate contents, nitrogen and phosphorus use efficiencies, ultrastructure and phytoremediation under Pb stress. When competition within the same sex was compared, females were more sensitive to Pb stress, while males possessed greater Pb contents, and a higher bioconcentration factor and tolerance index. Under inter-sexual competition, males alleviated competition effects through greater Pb absorption, and lower photosynthetic rates, nutrient use efficiencies and biomass accumulation. Moreover, Pb stress altered competition intensities of both sexes. Sex-specific competition and neighbor effects may regulate responses and phytoremediation under heavy metal stress in dioecious plants. In the future, more attention should be paid on the effects of inter- and intra-sexual competition on dioecious species in the process of forestation and restoration of contaminated soil.