Accumulation of phenolics and growth of dioecious Populus tremula (L.) seedlings over three growing seasons under elevated temperature and UVB radiation.

Accumulation of secondary metabolites may exhibit developmentally regulated variation in different plant organs. Moreover, prevailing environmental conditions may interact with development-related variations in plant traits. In this study, we examined developmentally regulated variation in phenolic accumulation in the twigs of dioecious Populus tremula (L.) and how the effects of elevated temperature and ultraviolet B (UVB) radiation on growth and phenolics accumulation varied as the plants get older. In an open-field experiment, six female and six male genotypes were exposed to single and combined elevated temperature and UVB radiation treatments for three consecutive growing seasons. The concentrations of low molecular weight phenolics and condensed tannins did not show age-dependent variation in the twigs. In temperature-treated plants, diameter growth rate decreased, and concentration of condensed tannins increased as plants aged; there were no cumulative effects of elevated UVB radiation on growth and phenolic accumulation. Females maintained a higher concentration of low molecular weight phenolics throughout the experimental period; however, growth and phenolic concentration did not vary over time in females and males. Our results suggest that phenolic accumulation in perennial plants may not necessarily always exhibit age-dependent variation and the effects of elevated temperature on growth and phenolic may diminish as plants get older.

Responses in growth and phenolics accumulation to lateral bud removal in male and female saplings of Populus tremula (L.) under simulated climate change.

The responses in growth and defense after tissue damage are highly variable in plants depending on species, damaged-tissue type and the intensity of damage. The prevailing abiotic conditions can also influence these responses. In this study, our aim was to examine how the removal of lateral vegetative buds affects the growth and accumulation of phenolics in saplings of the dioecious Populus tremula grown under simulated climate change. For three growing seasons, the saplings were grown under ambient conditions (control), elevated temperature (+2°C) and elevated UV radiation (30%) (UVB and UVA as its control), or a combination of these. In the fourth growing season, all saplings were grown under ambient conditions. The bud removal was performed twice - in summer and autumn - in the third year. The responses of growth and the accumulation of phenolics to the bud removal were measured at the end of the fourth growing season. Removal of 5% of the lateral buds resulted in higher leaf, stem and total plant biomass in both sexes of P. tremula saplings, compared to intact plants. The effects were greater in the temperature-treated plants, especially in the temperature-treated females. The concentrations of flavonoids and condensed tannins were higher in the bud-removed individuals. The concentration of condensed tannins was also higher in the males than in the females, opposite to the concentration of phenolic acids. There was no significant interaction between bud removal and UVB treatment on either growth or phenolics. Our results suggest that plants can allocate resources to both growth and defense simultaneously in response to tissue loss, and that global warming can modify the responses to some extent.

Elevated temperature and CO2 affect responses of European aspen (Populus tremula) to soil pyrene contamination.

High northern latitudes are climatic sensitive areas, and are also regions to which polycyclic aromatic hydrocarbons (PAHs) easily transport and accumulate with potential risk to natural ecosystems. However, the effect of PAHs on northern woody plant growth and defense under climate change is very little studied. Here, we conducted a unique experiment in greenhouses to investigate sex-related responses of the dioecious Populus tremula to pyrene (50mgkg-1) and residue of pyrene in soils under ambient and elevated temperature (+1.8°C on average) and CO2 (740ppm). Pyrene decreased stem biomass and leaf area by 9% and 6%, respectively under ambient conditions, and the reduction of leaf area was more severe under elevated temperature (38%), elevated CO2 (37%), and combined T+CO2 (42%). Other growth parameters were unchanged by pyrene. Pyrene did not affect the concentration of leaf total phenolics under ambient conditions, but increased it by 16%, 1%, and 20% compared to controls under elevated temperature, elevated CO2, and T+CO2, respectively. Pyrene had only minor sex-specific effects on plant growth and phenolics. The concentration of residual pyrene in pyrene-spiked soils was higher under elevated CO2 than under ambient, elevated temperature, and combined T+CO2. The results suggest that both sexes of P. tremula have the capacity to regulate growth and metabolism to adjust to the stress of the tested pyrene contamination under elevated temperature and CO2, but potential risk of pyrene to plants still exists in the future changing climate.

Sex-related responses of European aspen (Populus tremula L.) to combined stress: TiO2 nanoparticles, elevated temperature and CO2 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 nTiO2 contamination (0, 50, 300 mg kg-1) under elevated temperature (+1.6 °C) and CO2 (730 ppm), we conducted a study in greenhouses. Ti accumulated in roots exposed to nTiO2 (1.1-3.3 and 2.7-21.1 mg kg-1 in 50 and 300 mg kg-1 treatments, respectively). Elevated CO2 had no effects on Ti uptake, while elevated temperature increased it in the 300 mg kg-1 treatment. Males grew taller than females under ambient conditions, but females had greater height and biomass increment under elevated temperature. In all climate treatments, nTiO2 increased leaf phenolics in females by 12-19% and 15-26% at 50 and 300 mg kg-1, respectively. Leaf phenolics decreased under elevated temperature, but increased under elevated CO2 in both sexes. Results suggest that females have better chemical defense against nTiO2 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.