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Harvard Forest REU Symposium Abstract 2011
- Title: Diurnal Dynamics of Stem Conductance
- Author: Alena N Tofte (Harvard College (Harvard University))
- Abstract:
A plant’s ability to support growth, photosynthesize and sequester carbon effectively in variable environmental conditions is strongly dependant upon the dynamic capacity of water transport. Woody plants provide adequate whole-plant water supply through upward water movement from soil to crown within the plant’s vascular system. This system experiences negative pressure from stomatal transpiration, which thereby drives the upward movement of a continuous water stream. Diurnal variation in this tension gradient due to atmospheric conditions can induce cavitation, or the formation of gaseous embolisms within xylem conduits. These bubbles decrease the overall efficiency of water transport. Previous thought cites permanent elimination of the functionality of these affected vessels. However, some evidence has implied that cavitated conduits refill on a diurnal cycle. To address the ongoing debate surrounding refilling, we replicated an experiment from an earlier paper, published at Harvard Forest within the Holbrook Laboratory (Zwieniecki M.A. & N. M. Holbrook 1998, Plant, Cell & Environment. 21:1173-1180). We measured xylem hydraulic conductivity, percent loss of conductance and water potential on one ring-porous species (Fraxinus americana L., white ash) and two diffuse porous species (Acer rubrum L. red maple, Betula papyrifera Marsh., paper birch). Measurements were conducted in the afternoon between 1300 and 1400 hours, and were made again the following morning between 0600 and 0700 hours, June through July 2011 at Harvard Forest, Petersham, MA. Our results for ash corroborate previous results with preliminary evidence of refilling, while our results for maple and birch contrast results outlined in the 1998 paper. Possible explanations for this discrepancy include induction of embolism as an artifact of collection methodology, small sample size in the previous study, or natural variation in behavior due to differing climatic conditions between sampling years. Species-specific physiological capacities like diurnal embolism and refilling may determine rates of photosynthesis and carbon sequestration, tolerance of water stress, and associated geographic distribution with respect to water availability.
- Research Category: Physiological Ecology, Population Dynamics, and Species Interactions
