You are here

Harvard Forest >

Harvard Forest Symposium Abstract 2017

  • Title: Physiology of phloem loading in leaves of red oak trees
  • Primary Author: Jessica Gersony ()
  • Additional Authors: Meghan Blumstein (Harvard University); Morgan Furze (Harvard University); Uri Hochberg (); Michele Holbrook (Harvard Forest); Alexandre Ponomarenko (Harvard University); Andrew Richardson (Northern Arizona University); Fulton Rockwell (Harvard University)
  • Abstract:

    Red oaks have been characterized as passive loaders, raising the question of how assimilate export into the phloem is affected by diurnal fluctuations in leaf water potential. We made measurements of assimilation, leaf water potential, leaf NSC pools, and total osmolality in five mature red oak trees at Harvard Forest over a 24 hour period and used these data to estimate rates of carbohydrate export from the leaf into the phloem. Our data show that leaf sugar pools build up during the morning and then decline after midday, and that leaf starch pools build up until mid-afternoon, and then decline. Carbohydrate export occurs at maximal rates during the day, with the peak in export occurring slightly later than peak assimilation. There was a diurnal increase in leaf osmolality by 0.3 MPa (due to solute accumulation, not dehydration), which is only partially accounted for by the increase in soluble sugars. Work planned for the upcoming summer will focus on examining how leaf water potential, assimilation rate, and leaf NSC pools affect loading rates and also examine whether red oak exhibits heterogeneity of loading type.

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