The effect of elevated CO2 on the ecophysiology of mature Quercus robur in a temperate deciduous UK woodland.

Gardner, Anna (2023). The effect of elevated CO2 on the ecophysiology of mature Quercus robur in a temperate deciduous UK woodland. University of Birmingham. Ph.D.

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Atmospheric CO2 (Ca) is rapidly increasing and expected to reach, and perhaps surpass, over 550 μmol mol 1 by the middle of the 21st century. Rising Ca is the principal cause of human-induced global climate change and is primarily the result of anthropogenic activities such as fossil fuel burning and irreversible land-use change. However, the ocean and many terrestrial ecosystems take up and store carbon (C), therefore not all emitted CO2 stays in the atmosphere. The terrestrial biosphere has an important role in the C cycle yet there are large uncertainties in its response to future environmental change.
Forests are vital in the C cycle as they are large carbon stores with very large fluxes to and from the atmosphere. Forests are, therefore, important when considering the future atmospheric composition. In the northern hemisphere, temperate deciduous forests are considered to be particularly important carbon sinks yet there are still knowledge gaps regarding the responses of mature temperate forest ecosystems to elevated Ca and how this will affect the functioning of plants and ecosystems. Free-Air Carbon Enrichment (FACE) facilities enable us to assess and quantify the effects of elevated CO2 (eCO2) on whole patches of forest systems.
This thesis aims to enhance the knowledge base for the effects of eCO2 on the leaf-level physiology, biochemistry, and morphology of mature Quercus robur using a Free-Air Carbon Enrichment (FACE) facility at the Birmingham Institute of Forest Research (BIFoR). The objectives of this study are to quantify the photosynthetic performance, foliar nitrogen, and chlorophyll content, in oak leaves under simulated future (i.e., elevated) CO2 conditions. Additionally, a meta-analysis, including new data on Q. robur, was conducted to examine the stomatal responses across eCO2 experiments from 1999 to 2019 and assess the use of the optimal stomatal theory principles to characterise stomatal behaviour with eCO2.
This study, using tree canopy measurements, found that net photosynthesis (Anet) increased by 24% in mature Q. robur under eCO2 (150 mol mol 1 above Ca) and that photosynthetic enhancement was sustained across the first three years of CO2 fumigation at BIFoR FACE. There were no changes to foliar nitrogen (N) or chlorophyll under eCO2 exposure, but season and canopy position were found to be important influential factors when scaling leaf-to-ecosystem light harvesting and N allocation. The meta-analysis reported increases in intrinsic water use efficiency (iWUE) that were similar across the plant functional types (PFTs) that were assessed. There was no significant difference in stomatal responsiveness among the PFTs and no significant reductions in stomatal conductance (gs) with eCO2. Additionally, the optimal stomatal theory successfully characterised stomatal behaviour with eCO2 across a range of environmental conditions.
The research presented in this thesis extends the current knowledge on the physiological, biochemical and morphological responses of mature forest-grown trees in response to eCO2 and identifies the key environmental factors that influence the eCO2 response. The information presented contributes significant new knowledge that may be used by vegetation modellers (for the calculation of future carbon budgets) to help guide government policy developers and forest managers in decision making regarding climate change mitigation and to increase forest and environmental resilience to the effects of climate change such as with eCO2.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Life & Environmental Sciences
School or Department: Biological Sciences
Funders: None/not applicable
Subjects: G Geography. Anthropology. Recreation > G Geography (General)
G Geography. Anthropology. Recreation > GE Environmental Sciences
Q Science > Q Science (General)
Q Science > QK Botany
S Agriculture > SD Forestry


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