Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Understanding the coordination of hydraulic strategies with other traits in determining plant survival under drought

Auteur : Creek, Danielle

Université de soutenance : University of Western Sydney

Grade : Doctor of Philosophy (PhD) 2018

Résumé partiel
Drought negatively impacts plant growth and survival. The ability to maintain hydraulic functionality during water stress strongly influences whether plants will survive and recover from drought. Although our understanding of the mechanisms underlying drought-induced mortality have improved in recent decades, our understanding of the coordination between stomatal and hydraulic traits and their role in shaping drought resistance and enabling recovery remains poorly understood. In this thesis, I examined plant hydraulic traits across a range of contrasting species in order to better understand how hydraulics determines plant function under drought, governs gas exchange, and drives differences in drought resistance.
By subjecting three contrasting Australian tree species to water limitation, we were able to determine the hydraulic vulnerability to embolism of leaves, stems and roots as well as the relationship between stomatal conductance and photosynthesis with decreasing water potential. We found that leaves and/or roots were more vulnerable than stems in Eucalyptus coolabah and Acacia aneura, however E. populnea did not show vulnerability segmentation. Additionally, in these species stomatal closure always occurred prior to significant hydraulic dysfunction. We confirmed this finding in three additional tree species, Arbutus unedo, Ligustrum japonicum and Prunus persica via direct imaging of leaf embolism formation by the Optical Visualisation (OV) method with simultaneous measurements of stomatal conductance on intact plants.
Under long-term mild drought stress, E. coolabah and E. melliodora grown in a poly tunnel facility in large 75 L pots, were able to effectively maintain water potentials above thresholds likely to result in significant hydraulic dysfunction. However, when exposed to long-term severe drought stress, these species contrasted in their ability to avoid hydraulic dysfunction. Despite E. melliodora having more embolism resistantxylem and larger stomatal safety margins than E. coolabah, E. melliodora incurred the greatest hydraulic dysfunction during severe drought whereas E. coolabah was able to maintain leaf water potentials within a safe range by leaf shedding. This result suggests that xylem vulnerability alone is insufficient to predict a plant’s performance under drought.

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