PhD defence by Theresa Pflüger

To close or not to close? The role of stomatal density in regulating the response to combined heat and drought stress in wheat plants

Due to climate change with rising temperatures and water scarcity as well as a growing world population there is an increasing need to improve plant photosynthesis and productivity. Heat and drought episodes will occur more frequently in the future. Research into the effects of combined abiotic stresses is crucial to understand plant stress responses. One mechanism plants use to respond to environmental signals are stomata and their movement. Stomata are microscopic pores on plant surfaces, which facilitate the gas exchange of CO₂ and water vapour and regulate photosynthesis and water status. Stomata are obvious targets to improve crop performance under stress. In this PhD project, wheat (Triticum aestivum L.) cultivars with varied stomatal density were subjected to combined heat and drought stress experiments under constant and fluctuating light.

Based on the experiments, the genotypic variation in stomatal density influenced the stomatal responses under individual drought or combined heat and drought stress. Stomatal conductance (g_s) was the most sensitive parameter and decreased with drought stress despite expected stomatal opening due to simultaneous heat stress. Drought stress and stomatal closure were dominating the stomatal response irrespective of stomatal density, but mainly under constant light. Under fluctuating light, drought primarily reduced the magnitude of g_s, photosynthesis and transpiration but not the stomatal responsiveness, which was influenced by stomatal density. Low stomatal density led to a slower reaction to environmental change and higher g_s under combined heat and drought stress than high stomatal density. High stomatal density might better optimise photosynthesis and water use efficiency under stress. Under the progressive drought, the influence of stomatal density depended on the available soil water and not the duration of the drought stress, while under fluctuating light the intrinsic stomatal kinetics related to stomatal density were more important. Overall, stomatal responses to combined heat and drought stress could not be inferred from the individual stress responses.

Assessment Committee

Henrik Vlk Lütken, Associate Professor, Department of Plant and Environmental Sciences University of Copenhagen

Ebe Merilo, Associate Professor, Institute of Technology, University of Tartu

Bernd Wollenweber, Associate Professor, Department of Agroecology, Aarhus University

Supervisors

Eva Rosenqvist, Associate Professor, Department of Plant and Environmental Sciences, University of Copenhagen

Fulai Liu, Professor,Department of Plant and Environmental Sciences, University of Copenhagen

Time & venue

Thursday 27 February 2025 at 13:00

A8-18.02, Højbakkegård Allé 13, 2630 Taastrup and Hybrid/Zoom:
https://ucph-ku.zoom.us/j/62519100200?pwd=udQNM6Qk3mmlFHToGUqvlHNqi3wvJU.1

The defence is followed by a reception