Doctoral defence: Linda Rusalepp “The impact of environmental drivers and competition on phenolic metabolite profiles in hybrid aspen and silver birch”

On 22 November at 10:15 Linda Rusalepp will defend her doctoral thesis “The impact of environmental drivers and competition on phenolic metabolite profiles in hybrid aspen and silver birch” for obtaining the degree of Doctor of Philosophy (in Plant Ecology and Ecophysiology).

Supervisors:
Associate Professor Priit Kupper, University of Tartu
Dr. Anu Sõber
Professor Tõnu Püssa, Estonian University of Life Sciences

Opponent:
Associate Professor Virpi Virjamo, Eastern University of Finland

Summary
Plants are sessile organisms, which means they can’t escape from adverse growing conditions. As an adaptation, plants synthesise specialised metabolites (SM) – compounds that mitigate harmful environmental conditions, deter herbivores, pathogens, etc. The proportion of these metabolites in the metabolism of the whole plant can be very high, which can cause the plant’s growth rate to decrease. The focus of this study is on phenolic compounds, like flavonoids and tannins, found in all plant species. Most studies on the relationships between plant SM and environmental conditions have been conducted in growth chambers. However, the changes in plant SM are better studied in field experiments in which both abiotic and biotic factors influence the plant simultaneously. The aim of this thesis was to investigate the impact of competition and environmental conditions on the SM of hybrid aspen (Populus tremula L. × P. tremuloides) and silver birch (Betula pendula) trees growing in field conditions. The results showed that competitively suppressed trees were more susceptible to different environmental drivers than dominant trees were. Extensive thinning had a strong effect on the phenolic content of competitively suppressed hybrid aspen, whereas thinning didn’t affect the SM content of dominant residual trees. The phenolic profile of suppressed trees also reacted more strongly to changes in mean annual temperature. In addition, it was found that the content of hydroxybenzoates and condensed tannins in both leaves and roots was a good predictor of stressful conditions, while the content of flavonoids in leaves was strongly related to light intensity. The SM profiles illustrated the different needs for protection against irradiance possessed by suppressed and dominant trees, as well as illustrating different resource supply. The long-lasting effects of extensive thinning on suppressed residual tree SM profiles, as well as the fact that SM synthesis is an additional cost at the expense of tree growth, should be considered in forest management practises.