HOW PLANTS MANAGE EPISODES OF DROUGHT STRESS: FROM SIGNALING TO EMBOLISM RESISTANCE OF PLANT ORGANS
Huber, Annika Erika
Water shortage is the most limiting factor for plant growth and development. Nevertheless, the current state of science is far from understanding drought stress behavior in plants and the mechanisms leading to drought stress resistance. This thesis investigates long-distance signaling types (hydraulic, electrical, chemical) preceding the onset of stomatal closure, studies the role of hydraulic integrity of plant organs (root, stem, petiole) during and after drought stress periods on stomatal conductance, and investigates xylem network characteristics that determine hydraulic efficiency (hydraulic flow per unit xylem area) and embolism resistance. In the first study, I exposed sunflowers (Helianthus annuus) to two different drought stress treatments and measured simultaneously and continuously stomatal conductance, acoustic emissions events (AE), and surface-level electrical signals. Changes in organ-level water potential and leaf-level abscisic acid (ABA) concentration were also measured on a subset of plants throughout the experiment. I found that hydraulic signals precede the onset of stomatal closure while surface potentials shifted concurrently with the onset of stomatal closure. Leaf-level ABA concentration did not change until after stomata were closed. In the second study, six different plant species (Helianthus annuus, Populus x canadensis, Acer saccharum, Acer saccharinum, Picea glauca, Tsuga canadensis) were exposed to increasing drought stress intensities with subsequent rewatering events. At each drought intensity, I measured water potential, relative water content, and embolism thresholds of roots, stems, and petioles using cryo-microscopy and single vessel injection technique. These results were compared to established hydraulic vulnerability curves (PLC curves). Results showed that leaf petiole xylem vessels were the most susceptible to embolism formation, while root and stem xylem vessels were highly drought resistant. Stomatal closure was not correlated to xylem cavitation events since cavitation only occurred during higher drought stress intensities. After rewatering, embolism events in the petiole xylem vessels recovered for all species, while poplar plants shed their leaves. In Acer saccharum we found that stem xylem vessel embolism increased after rewatering. Additionally, I found a disparity between PLC curves and plant organ water potentials experienced during drought periods. Lastly, xylem networks of three ring- (Quercus montana, Fraxinus pennsylvanica, Carya ovata) and three diffuse-porous tree species (Fagus sylvatica, Liriodendron tulipifera, P. x canadensis) were reconstructed to understand the topology of vascular networks. Fluid simulation models of each network were performed to predict the resistance of hydraulic conductivity as a function of vessel dropout within the network. I found that the combination of different network presentations advanced the understanding of xylem networks. Additionally, xylem dropout analysis revealed that all six examined xylem networks experience a 50% loss in hydraulic conductivity with a xylem vessel dropout fraction between 0.01-0.04%, despite the degree of xylem vessel connectivity differing among the tree species.
xylem network; Horticulture; Plant sciences; drought; drought signaling; embolism; plant hydraulics; stomatal closure
Bauerle, Taryn L.
Setter, Timothy Lloyd; Pineros, Miguel Alfonso
Doctor of Philosophy
Attribution-NonCommercial-NoDerivatives 4.0 International
dissertation or thesis
Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivatives 4.0 International