Modelling phloem and xylem transport within a complex architecture

The function of the plants vasculature, incorporating both phloem and xylem, is of fundamental importance to the survival of all higher plants. While the physiological mechanism involved in these two transport pathways has been known for some time, quantitative modelling of this has been slow to develop. 1-D continuous models have shown that the proposed mechanisms are quantitatively plausible (Thompson & Holbrook 2003), but more complex geometries (architectures) have remained out of their reach because of mathematical difficulties. In this work we extend the alternative, modular approach of Daudet et al. (2002) by using recently developed numerical tools which allow us to model complex architectures. After a full description of the extended model, we first show that it efficiently reproduces the results of the continuous approach when applied to the same simple configurations. The model is then applied to a more complex configuration with two sinks, confirming that sink priority is an emergent property of the Münch flow as earlier found with a minimalistic model (Minchin et al. 1993) that had been criticized for ignoring some biophysical properties of phloem transport. It is further shown how source leaf transpiration can change the relative carbon allocation rates among sinks.