The CEE Department is pleased to announce Danlyn Brennan's MS Thesis Defense: "Modeling Leaf-Level Transpiration: Exploring the Consequences of Assumed Saturated Vapor Pressure in Leaves"
Date: Monday, June 5th, 2023
Time: 11:30 AM
Location: EB 310 or Zoom: pdx.zoom.us/j/87508874474
Advisor: Dr. Samantha Hartzell
Abstract: "Understanding the dynamics of water transport through leaf intercellular airspaces (IAS) and its impact on transpiration is crucial for accurate predictions of plant water use and ecosys- tem response to changing climates. This study investigates the implications of assuming undersaturation of water vapor in the IAS for transpiration predictions and explores potential modifications to standard modeling approaches.
A dynamic 1D soil-plant-atmosphere continuum using a stomatal optimization model (SPAC-SOT) framework was used to simulate the response of tree species, Pinus edulis, to prolonged drought and varying environmental conditions. Comparisons between two model assumptions (saturated vs. undersaturated IAS) reveal notable differences in transpira- tion and carbon assimilation predictions, particularly when soil moisture and vapor pressure deficit (VPD) is low. Assuming saturation in the IAS leads to an overprediction of transpiration and carbon assimilation as compared with the undersaturated model, suggesting the need for accurate representations of the leaf area index (LAI) and xylem characteristics such as maximum hydraulic conductance (Kp,max) to capture embolism and mortality risk, as well as canopy-level water vapor fluxes influencing global climate conditions.
Through sensitivity analysis, it is found that certain plant parameters significantly influence the maximum rate of water loss through transpiration, highlighting the model's sensitivity to these factors. The LAI parameter emerges as a key factor affecting transpiration under both saturated and undersaturat- ed conditions, while the Kp,max parameter plays a vital role in carbon assimilation. Finally, cuticular conductance, gcut, strongly affects the extent to which model results diverge.
The study underscores the importance of leaf-level assump- tions in shaping larger-scale water cycles, particularly in the context of ongoing droughts and evolving climates. By refining modeling approaches to incorporate undersaturation in the IAS, our understanding of plant water use efficiency, drought tolerance, and ecosystem responses can be advanced, aiding in more accurate predictions of future water resources and climate dynamics."