Abstract
In this paper, we present and use a coupled xylem/phloem mathematical model of passive water and solute transport through a reticulated vascular system of an angiosperm leaf. We evaluate the effect of leaf width-to-length proportion and orientation of second-order veins on the indexes of water transport into the leaves and sucrose transport from the leaves. We found that the most important factor affecting the steady-state pattern of hydraulic pressure distribution in the xylem and solute concentration in the phloem was leaf shape: narrower/longer leaves are less efficient in convecting xylem water and phloem solutes than wider/shorter leaves under all conditions studied. The degree of efficiency of transport is greatly influenced by the orientation of second-order veins relative to the main vein for all leaf proportions considered; the dependence is non-monotonic with efficiency maximized when the angle is approximately 45° to the main vein, although the angle of peak efficiency depends on other conditions. The sensitivity of transport efficiency to vein orientation increases with increasing vein conductivity. The vein angle at which efficiency is maximum tended to be smaller (relative to the main vein direction) in narrower leaves. The results may help to explain, or at least contribute to our understanding of, the evolution of parallel vein systems in monocot leaves.
Highlights
IntroductionThe dicot group of angiosperms, have evolved complicated hierarchical venation systems
Vascular plants, the dicot group of angiosperms, have evolved complicated hierarchical venation systems
We address the question of what is the resulting distribution of sucrose (a 2D leaf area concentration map) and the resultant hydraulic pressure pattern across the leaf, where the latter is used here as an index that characterizes the transport of both water and sucrose out of the leaf
Summary
The dicot group of angiosperms, have evolved complicated hierarchical venation systems. The first-order so-called main vein of the system enters the leaf at the petiole and extends to the apex. Second-order veins diverge from this first-order vein. Higher order veins branch off from their lower order neighbors to form a complex reticulated vein network extending across the entire leaf (Esau, 1953; Sack and Scoffoni, 2013). It is generally accepted that the whole-of-plant hydraulic system is significantly influenced by the hydraulic conductance of the plant’s leaves (Sack and Holbrook, 2006). It follows that leaf vasculature plays an important role in the response of a plant to water stress. A plant has come to utilize this physical infrastructure to translocate to the rest of the plant, via a parallel phloem system connected to the petiole, photosynthetic products produced across the leaf (Roth-Nebelsick et al, 2001)
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