Abstract

DONNELLY, TALLIS M. Water Loss Exceeds Uptake in Burning Trees, But May Not Be Sufficient to Cause Whole-Plant Hydraulic Failure. It has been recently recognized that hydraulic dysfunction may be an underappreciated contributor to tree mortality following some fires. The heat plume hypothesis proposes that fire can produce hydraulic dysfunction via cavitation, due to high water loss resulting from high vapor pressure deficit that develops above the flames. This mechanism is distinct from fire damage resulting from direct incineration or lethal temperatures. It is not clear whether the plant water pathway remains sufficiently functional during burning to allow enough water loss to cause substantial plant water deficits. Here, I measured water uptake during and after burning to test (i) whether the water transport pathway remained intact and functional under burn conditions, (ii) if the loss of water during burning was great enough to potentially induce acute water deficit in the rest of the plant, and (iii) how these responses may vary across species. I recorded water uptake in eight species before and during burning, and I characterized post-burn water uptake patterns in two of those species that had contrasting functional traits. Burning resulted in an average 24-fold increase in water uptake across all species. Water transport continued during and after burning, indicating that xylem function was sustained, at least to some extent. However, water uptake represented only a small fraction of leaf water lost during burning, indicating that some loss of function did occur. Overall, water uptake during burning was equivalent to only 6% of total water in the leaves of the sample, revealing that water supplied to terminal branches during burning is small, relative to the total amount of water in the plant. There were significant differences across species in the magnitude of water uptake during burning which were not explained by specific leaf area, leaf water content, deciduousness, or wood type (ringor diffuse-porous). My results show that the heat plume hypothesis is applicable across a wide range of species and burn conditions, but that the resulting water losses may not be sufficient to result in whole-plant mortality. Water Loss Exceeds Uptake in Burning Trees, But May Not Be Sufficient to Cause Whole-Plant Hydraulic Failure. by Tallis M. Donnelly A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science