Phloem sap flow and carbohydrate transport in vascular plants: A generic surface model

Plant leaves produce carbohydrates that are distributed throughout the organism via the phloem pathway. Understanding how phloem transport operates is essential to simulate patterns of growth activity and carbon allocation within trees. In agreement with Münch´s hypothesis, we model phloem sap motion as a pressure flow. This is a single-solute (sucrose) model. It solves diffusion-like equations using finite element analysis on a triangulated surface that represents the phloem. In this study, we show that the surface model is compatible with representing architecturally complex structures like trees. The model also takes into account the effect of grain orientation on translocation. Simulating sap flow at a branchstem junction highlights that carbohydrates move dominantly along the longitudinal direction of phloem fibres. However, lateral transport remains a major unknown in the current understanding of assimilate transport in plants.