Public defence in forestry industry production systems: Diana Eckert
Title: Refixation of respiratory CO2 in leaves
Subject: Forestry industry production systems
Faculty: Faculty of Technology
Date: Friday 13 November 2020 at 1.00 pm
Place: Via Zoom: https://lnu-se.zoom.us/j/63309050428?pwd=Q29xSFVhVjhuR1IrUjlVYis1eEpBdz09
External reviewer: Professor John Marshall, Swedish University of Agricultural Sciences, Sweden
Examining committee: Associate professor Anders Ræbild, University of Copenhagen, Denmark
Professor Douglass F Jacobs, Purdue University, USA
PhD Sanna Annika Sevanto, Los Alamos National Laboratory, USA
Chairperson: Professor Jimmy Johansson, Department of Forestry and Wood Technology, Linnaeus University
Main supervisor: Associate professor Anna Monrad Jensen, Department of Forestry and Wood Technology, Linnaeus University
Assistant supervisors: PhD Helle Juel Martens, University of Copenhagen, Denmark
Associate professor Johanna Witzell, Swedish University of Agricultural Sciences, Sweden
PhD Lianhong Gu, Oak Ridge National Laboratory, USA
PhD Daniel C Dey, USDA-FS, Northern Research Station, USA
Examiner: Professor Johan Bergh, Department of Forestry and Wood Technology, Linnaeus University
Spikning: Friday 23 October at 1.15 pm at the University Library in Växjö
Abstract
Photosynthesis is a vital process for trees, one in which CO2 plays a major role. At the same time, in their mitochondria, trees themselves produce CO2 In this PhD thesis, I investigated the fate of respiratory CO2 – is it all released back into the atmosphere or is it re-used in photosynthesis? By modeling the percentage of respiratory CO2 that is being refixed in photosynthesis (Pr), Pr was explored in many situations. This thesis examined the effects on Pr of physiological, anatomical, and morphological traits; variations between species, functional groups or biomes; and light and temperature levels. In addition, an experimental study explored the effect of drought on carbon allocation, which implied potential advantages of high Pr.
The main findings are that trees that have high internal diffusion resistance (rm), that have closed more of their stomata, and that have high photosynthetic capacity which can draw on CO2 molecules are better at trapping and using respiratory CO2. Consistent with this, I found that conifers, and boreal biomes overall, refixated the most. This group, with its hardy evergreen leaves, has particularly high leaf mass per area and cell wall thickness. These two traits are known to result in high rm, and they also positively correlated with Pr in my data. Species with high Pr might be less dependent on uptake of atmospheric CO2 and can close more of their stomata to conserve water. Models calculating terrestrial CO2-uptake should therefore consider including Pr, and assume that plants with high rm refixate most of their respiratory derived CO2. For example, drought during early development of P. mariana shoots affected growth in such a way that carbon was allocated away from structural components. This might result in mature shoots with lower rm, which could reduce their Pr permanently. If this is true, new shoots with less efficient refixation might make the tree as a whole less resilient during future droughts. The implications are that while the higher Pr of boreal biomes and evergreen conifers may make them better able to tolerate future dry-periods, such periods may weaken this effect if they happen during shoot development.
Keywords: CO2 refixation, mesophyll resistance, stomatal conductance, Vcmax, leaf anatomy, photosynthesis, forestry, carbon allocation, ecophysiology