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

Responses of growth and leaf phenolics in European aspen (Populus tremula) to climate change during juvenile phase change

In trees, the change from juvenile to adult vegetative phase can last for years. In Populus tremula L., this phase change is characterized by a morphological change in leaf shape, as leaves in the seedling phase typically are sharp-tipped, while saplings and trees have round-tipped leaves. In an open-field experiment, we studied the separate and combined effects of enhanced temperature and UVB radiation on 2-year-old P. tremula plantlets undergoing phase change. The concentration of salicylates was higher in the seedling-phase plants than in tree-type plants. In contrast, the concentration of condensed tannins was higher in the tree-type plants but only under ambient temperature. Enhanced temperature increased growth of the plants and the concentration of some salicylate compounds, and it decreased concentrations of flavonoids, phenolic acids, and condensed tannins. In addition, in the seedling-phase plants, the severity of rust infections decreased and herbivore damage increased under warming. The effects of enhanced UVB radiation were weaker, as concentrations of only two flavonoid compounds increased under enhanced UVB radiation. Based on our results, climate change may have a moderate delaying effect on the physiological development of both sexes of P. tremula, which may lead to lowered performance in their normal habitat in the future.201