Sex-related responses of European aspen (Populus tremula L.) to combined stress: TiO nanoparticles, elevated temperature and CO concentration.

The combined effects of climate change and chemical contaminants on plant performance are still not well understood. Especially, whether different sexes of dioecious plants respond differently to combined stresses is unknown. In order to study the sex-related responses of European aspen to soil nTiO contamination (0, 50, 300 mg kg) under elevated temperature (+1.6 °C) and CO (730 ppm), we conducted a study in greenhouses. Ti accumulated in roots exposed to nTiO (1.1-3.3 and 2.7-21.1 mg kg in 50 and 300 mg kg treatments, respectively). Elevated CO had no effects on Ti uptake, while elevated temperature increased it in the 300 mg kg treatment. Males grew taller than females under ambient conditions, but females had greater height and biomass increment under elevated temperature. In all climate treatments, nTiO increased leaf phenolics in females by 12-19% and 15-26% at 50 and 300 mg kg, respectively. Leaf phenolics decreased under elevated temperature, but increased under elevated CO in both sexes. Results suggest that females have better chemical defense against nTiO than males under future climate conditions. In the longer run, this may cause changes in the competitive abilities of both sexes, which again may affect sex ratios and genetic variation in nature.