A theoretical and empirical framework for measuring minimum conductance, an understudied plant drought trait

Irlam, Huw

A theoretical and empirical framework for measuring minimum conductance, an understudied plant drought trait

Thesis / Dissertation

2025

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

In light of increased drought frequency and intensity due to climate change, knowledge of how plant drought tolerance is affected is important for understanding plant vulnerability to these changes. Minimum conductance (gmin) describes the residual rate of water loss by a plant through its leaves when it has closed its stomata in order to minimise that water loss rate. This includes contributions to water loss through incompletely closed or leaky stomata, the waxy cuticle layer, or through wounding and scarring. This understudied conductance parameter is a critical piece to understanding plant dry-down time to death. However, definitions of this trait have historically been inconsistent leading to non-standardised methods for measurement, which lack an underlying theoretical basis. This obscures assessment of the existing variability and sensitivity of this important trait. In this thesis, clear definitions for minimum conductance are provided. A theory-based and biologically meaningful framework for measuring this trait over the stomatal safety margin is proposed. There is a focus on standardisation of existing methods, while increasing applicability and reproducibility on plants with a variety of morphologies. Using this framework, an assessment of minimum conductance was carried out on three characteristic and well-studied plant families of the Cape Floristic Region, namely Proteaceae, Ericaceae, and Restionaceae, to improve our understanding of drought response in these groups while demonstrating how this framework helps to improve minimum conductance measurements. Results showed a diverse response of minimum conductance values indicative of diverse drought strategies. This highlights the importance of including accurate values of minimum conductance in models predicting plant mortality under changing climate conditions.

Keywords

Plant drought

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