Tree-soil-water relations under elevated CO\(_2\) – following the flow

Quick, Susan Elizabeth (2026). Tree-soil-water relations under elevated CO\(_2\) – following the flow. University of Birmingham. Ph.D.

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Abstract

The climate background to increasing atmospheric carbon dioxide levels alongside other greenhouse gases is described. The effects of these climatic drivers and the broad picture of other related climate impact is outlined. Proportions of carbon-cycle emissions and sinks within the landscape are noted. The relationships between the Water cycle, Carbon cycle and Energy cycle are considered, in particular the water, carbon, energy balance approach used within global climate models.

The role of forests in contributing to emissions and as a sink for carbon is described as a background to the Birmingham Institute of Forest Research Free-air CO\(_2\) enrichment (BIFoR FACE) experiment is described. This project, juxtaposed amongst other related research projects, contributes novel research topics embracing plant-water related themes within this large experiment. The Soil-Plant- Atmosphere continuum model is used to focus the thesis work as a whole.

Firstly, it tackles the enhancement of knowledge concerning daytime transpiration of large (>10cm DBH) mature trees of Quercus, Acer and Crataegus species, under climatic changes within the BIFoR FACE experiment across the three treatment types: elevated carbon dioxide (eCO\(_2\)), ambient carbon dioxide (aCO\(_2\)), no-infrastructure control (Ghost). The measurement of stem xylem sap flow ( as a proxy for whole canopy transpiration) in these trees produces both new processed data relating to daytime tree water usage and also sub-daily sap flux data demonstrating tree xylem dynamics under the three experimental conditions across seven seasons of treatment from year1 (2017) to year 7 (2023).

Secondly soil water volumetric water content (VWC) and temperature data are collected for the same seven seasons, enabling relations between soil and plant to be explored. This exploration is facilitated by using the relative extractable water transformation of soil-water data down to one metre soil depth. Again findings and results from the differing timescales (30-minute, day, month, season, year) are considered and compared with the tree-water results.

Finally leaf measurements of stomatal conductances (enabling leaf transpiration calculation) and leaf temperatures are presented enabling comparison of the three tree species differences and similarities. Sub-daily dynamic patterns of leaf transpiration are compared with the sap flux results for oak and extraction of potential storage water usage available to the leaves is reported for this species.

The broad nature of this study highlights some benefits and limitations of the new knowledge which can be extracted from our manipulation experiment and illustrates how lateral thinking can assist in making effective use of novel data.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):