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Gent University (2019)

Improved insights into carbon fertilization and drought in Populus tremula through medical imaging

De Backer Klaas

Titre : Improved insights into carbon fertilization and drought in Populus tremula through medical imaging

Auteur : De Backer Klaas

Université de soutenance : Gent University

Grade : Master of Science in Bioscience Engineering : Agriculture 2019

Résumé
Nowadays, the effects of climate change are becoming more and more apparent in our surroundings. Temperature records keep piling up, heat waves are omnipresent, prolonged drought periods and intense precipitation are witnessed and many more. Extreme weather events like this will increasingly occur as atmospheric CO2 concentration ([CO2]) keeps on rising. Trees and forests are, among others, affected by these climatic changes. Recent studies have shown that massive tree die-off events have increased in frequency, however, there are still major scientific uncertainties in our understanding of climate-induced changes in trees and forests, making the question of how plants will cope with e.g. drought stress in the future a topic of intense debate and urges the need for profound research. To better understand the effects of climate-induced drought on trees, we investigated the phloem functioning of Populus tremula L., under enhanced [CO2], in combination with imposed drought. The Populus tremula L. was chosen because it is a widespread and eco logically important tree species of temperate and boreal forests in Eurasia. Two Populus tremula L. trees were grown in treatment chambers under ambient (TA : [CO2] of ± 409 ppm) or elevated (TE : [CO2] of ± 700 ppm) conditions, whereby ample soil water was at their disposal. The Populus tremula tree grown under CO2 fertilisation showed faster stem growth and larger leaf area development. Due to the difficulty of examining phloem cells because of it’s sensitivity to perturbations, direct in vivo measurements are necessary. Such phloem measurements are quiet complex, with the result that only limited data of direct measurements of phloem dynamics exist. In this thesis, positron emission tomography (PET), a nuclear medicine functional imaging technique, was used to assess the influence of climate change on phloem transport. Hereby, a combination of labeled 11CO2 (with 11C being a short-lived carbon isotope with a half-life of 20.4 min) in a PET-scanner for small animals and compartmental modelling was used to assess the influence of climate-induced drought on phloem transport. Measurements on both trees grown under ambient and elevated [CO2] started off in their native well-watered state. Subsequently, the trees were subjected to sudden drought. During this drought, mea iii surements were performed on a regular basis to follow up any changes in phloem transport.

Mots clés : Climate change, CO2, Drought, 11C, Positron emission tomography, Plant PET scanning, Populus tremula L., Phloem, Phloem transport characteristics

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