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Harvard Forest Symposium Abstract 2014

  • Title: Assimilate Translocation in Trees: Are source-to-sink pressure gradients large enough to move sugars from leaves to the roots?
  • Primary Author: Michael Knoblauch (Washington State University)
  • Additional Authors: Michele Holbrook (Harvard Forest); Jan Knoblauch (Harvard University); Jessica Savage (Harvard University Faculty of Arts and Sciences)
  • Abstract:

    The energy rich substances generated by photosynthesis are sugars, which are the basis for almost all life on earth. These sugars are translocated throughout plants from sites of generation, to sites of storage and consumption (e.g. fruits, roots). This transport takes place in a specialized tissue called phloem which contains tube like cells. Despite more than a century of research, the process of sugar loading and transport is not yet clear. Especially in trees, the long distance of translocation challenges current hypotheses. In particular, it is unclear whether the pressure gradients between sources and sinks are large enough to drive flow through the phloem at measured rates based on estimates of the hydraulic resistance of the sieve tubes that incorporates the structure of the sieve plates. This project aims to investigate phloem transport in large trees by measuring critical parameters such as phloem sap viscosity, flow velocity, tube geometry, and tube pressure. The combination of data will allow the evaluation of current hypotheses on phloem transport and will provide important knowledge for various fields such as plant physiology, plant insect interactions, and forest ecology.

  • Research Category: Forest-Atmosphere Exchange