MODELLING THE EFFECT OF XYLEM AND PHLOEM TRANSPORT ON LEAF GAS EXCHANGE

Whole tree water and carbon relations are mediated between the leaves and carbon sinks in the form of water potential and osmotic concentration through long distance xylem and phloem transport within the tree.
Here we present a whole tree level model which couples these source, sink and transport processes.
We demonstrate how xylem and phloem transport capacity, together with soil water and sink sugar status, set limits to the maximum leaf gas exchange that can be sustained by a plant in steady state.
We further show that when down-regulation of photosynthetic capacity depending on leaf sugar concentration is added to the model formulation, the typically observed stomatal behaviour in relation to environmental drivers and sink status can be qualitatively understood by maximization of the simultaneous photosynthesis production.
In our steady state formulation, the rate of photosynthetic production equals the phloem transport rate, and the rate of sugar utilization in the sinks.

IX International Workshop on Sap Flow

T. Hölttä, E. Nikinmaa

CO₂ assimilation, cavitation, phloem, photosynthesis, stomatal conductance, transpiration, xylem

https://doi.org/10.17660/ActaHortic.2013.991.43