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Harvard Forest REU Symposium Abstract 2005
- Title: Influence of photosynthetic rates on xylem ionic content and hydraulic resistance
- Author: Melissa R Whitaker (Prescott College)
- Abstract:
Water transport through vascular plants is believed to be an entirely passive process, with stomata providing the only mechanism by which plants could control the movement through the xylem. However, it has recently been shown that the hydraulic resistance of detached stem segments is affected by the concentration of ions, such that higher KCl concentrations can significantly increase the flow rate of water over a very short time scale. This alteration results from interactions between ions and the hydrogels located in the bordered pit membranes between xylem vessel elements. Ions shrink these hydrogels, thereby increasing the diameter of the channels between vessels and decreasing xylem hydraulic resistance. This mechanism has profound implications for plants to mediate flow rates in response to environmental variation, though the extent to which plants employ this mechanism is unknown. To investigate the regulation of hydraulic resistance within the canopy, sugar maple (Acer saccharum) saplings were sampled at three sites within the Harvard Forest. Photosynthetic rates were measured on branches in sun and shade, and sap from these branches was collected and analyzed for K+ concentration. A correlation between photosynthetic rates and K+ content of xylem sap was observed. Branches in direct sunlight and with higher photosynthetic rates contained significantly (p<0.05) higher concentrations of K+ in their sap than branches from shady or predawn conditions. This supports the suggestion that plants actively mediate hydraulic resistance within the canopy, providing them with a mechanism for adjusting their hydraulic architecture in response to microclimatic heterogeneity.
- Research Category:
