Doctoral defence: Marili Sell “The impact of environmental change on ecophysiology of hemiboreal tree species - acclimation mechanisms in belowground”

On 9 December at 10:15 Marili Sell will defend her doctoral thesis “The impact of environmental change on ecophysiology of hemiboreal tree species – acclimation mechanisms in belowground” for obtaining the degree of Doctor of Philosophy (in Plant Ecology and Ecophysiology).

Supervisors:
Associate Professor Priit Kupper, University of Tartu
Professor Ivika Ostonen-Märtin, University of Tartu

Opponent:
Jouni Kilpeläinen, Natural Resources Institute Finland (Finland)

Summary
By the end of this century, the predicted increase in air temperature and precipitation in Northern latitudes will lead to an increase in relative air humidity. Previous studies have shown a decrease in the growth rate of trees. Higher humidity decreases the transpiration rate, which diminishes the force facilitating water and nutrients towards roots. We have limited information on how these changes affect plant roots and water or nutrient cycles in soil. When nutrient availability in soil decreases, trees’ fine roots change their shape and form of new roots, and with the increasing absorptive area, the uptake of nutrients is enhanced. In addition, roots can exude different organic compounds into the soil, which is a food source for soil microbes. These microbes on roots and in the rhizosphere can meediate the necessary mineral nutrient uptake for plants. Measuring these root exudates is difficult, and the effects of environmental changes are unknown. In this study, we analysed the acclimation mechanisms of five tree species to high humidity and different nitrogen forms in soil. We measured how much fine root carbon exudation depends on the functional share of absorptive, pioneer and transport roots, which are all fine roots. Additionally, we implemented smart technologies to measure fine root growth dynamics by taking pictures with mobile phones and analysing the images with machine-learning-based software. Novel outcomes from this study include: 1) fine roots exude substantial amounts of carbon into soil, which is related to plant physiological parameters; 2) future studies measuring fine root exudates should consider root functional distribution and growth of some tree species was less affected by increased air humidity; 3) constant high humidity can change the development of fine roots, intensify root senescence and increase the absorptive area in fine roots; 4) the combination of smartphones and deep-learning methods is easy, fast and accurate to measure fine root growth in growth chambers.