Sexual differences in above- and belowground herbivore resistance between male and female poplars as affected by soil cadmium stress

Abstract

Dioecious plant species presented sexual differences in metal accumulation and allocation between male and female conspecifics that grown on metal contaminated soil. As the Elemental defense hypothesis postulates that metals accumulated in plant tissues could protect plants from herbivory, whether such sexual dimorphism in response to metal stress of a dioecious plant will lead to differences in herbivore resistance between male and female conspecifics is still unknown. In this study, we used female and male siblings of Populus deltoides to investigate the effect of plant sex on the growth and feeding preferences of four leaf herbivores and a root herbivore under soil cadmium (Cd) stress. The results showed that the male plants accumulated significantly higher Cd in the leaves while the females allocated more Cd in the roots. Leaf herbivores fed on male leaves grew worse than those fed on female leaves under Cd exposure, while the root herbivore showed the opposite results. In addition, all leaf herbivores strongly preferred the leaves from Cd-stressed female plants than male ones. The quantification of gene expression further showed that Cd stress could significantly upregulate more genes involved in Cd uptake, transport and detoxification pathways in male leaves and female roots. In combination with the correlation tests, we postulated that such sexual differences in herbivore resistance between the two plant sexes was most likely due to the different Cd allocation patterns in plant leaves and roots.