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Harvard Forest REU Symposium Abstract 2008

  • Title: Hydraulic Mechanisms Controlling Leaf Senescence in Sugar Maple (Acer saccharum Marsh.) and Red Oak (Quercus ruba)
  • Author: James B Onstad (Harvard University)
  • Abstract:

    It remains poorly understood which physiological, environmental and endogenous factors contribute to the onset of leaf senescence. Understanding how senescence is triggered in leaves is crucial to incorporating leaf fall into ecosystem models and carbon flux scenarios. Recent research suggests that a decline in the conductance of the liquid phase of water through leaves (Kleaf; mmol m-2 s-1 Mpa-1) is correlated to leaf senescence. It has been hypothesized that a decline in Kleaf triggers leaf senescence by reducing the delivery of xylem-transported compounds such as nitrogen and cytokinins to the leaf. We tested the hypothesis that a decline in Kleaf acts causally to trigger leaf senescence. Our measurements of Kleaf and leaf chlorophyll concentrations in Sugar Maple (Acer saccharum Marsh.) and Red Oak (Quercus rubra) during the spring and summer of 2008 suggest that a decline in Kleaf precedes leaf senescence. Using humidity chambers to lower Kleaf without altering photosynthetic radiation we were able to significantly decrease the concentration of chlorophyll in Red Oak leaves (P < 0.05). These preliminary results provide evidence that Kleaf acts as a determiner of leaf senescence. An attempt was made to determine the role that petiole and lamina conductance play in decreasing Kleaf. Our data indicate that lamina conductance plays the determining role in Kleaf variability, but we recommend that more effective techniques need to be developed in order to examine the respective role that petiole and lamina conductance play in altering Kleaf. Finally, an investigation into the effect of Kleaf on the delivery of compounds known to regulate senescence should be carried out on these two species.



  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions