Hydrodynamic Modelling Study of Angiosperm Leaf Venation Types

Abstract

The morphology of leaf venation has been studied repeatedly and various systems have been proposed for the classification of the observed leaf venation patterns. Almost nothing is known, however, about the functional properties of the various venation types. Using a computer modelling approach we analysed the water transport properties of typical craspedodromous and brochidodromous venation patterns. The water transport through the leaf and the veins was modelled as a fluid flow through a porous medium and the mathematical model was solved with the Finite Element Method. The simulations illustrate that the leaf margin represents a critical region in terms of water supply. The results provide a plausible functional explanation for three well known phenomena: 1) the correlation between craspedodromous venation and the formation of leaf teeth; 2) the fact that craspedodromous venation is more common in temperate than in tropical regions and 3) the fact that xeromorphic leaves tend to have more closed venation.

Correlations of climate and plant ecology to leaf size and shape: potential proxies for the fossil record

“…This is the first time that relationships between leaf physiognomy and leaf economic variables have been quantified, and they have a plausible underlying explanation. The development of large teeth is only possible if leaf expansion is rapid (Roth et al, 1995;Mosbrugger and Roth, 1996), and fast growth correlates with high nitrogen content, low leaf mass per area, and other variables on the ''quick'' end of the leaf economics spectrum (Wright et al, 2004). This mechanistic link may also explain why correlations with character states not related to tooth area (e.g., number of teeth) are not as strong.…”

Causes of ecological gradients in leaf margin entirety: Evaluating the roles of biomechanics, hydraulics, vein geometry, and bud packing

“…Mechanical and hydraulic independence of the areas supported and supplied by individual secondary veins means that those areas should taper distally, like leaves supported by a midrib, thus favoring marginal teeth in thin leaves. Simulations suggest that hydraulic supply can be critically limiting at the leaf margin; hydraulically vulnerable areas-that is, those far from secondary veins near their tips, on the leaf margin-are absent in toothed leaves ( Roth et al, 1995 ). A completely diff erent argument, based on minimizing the costs of supportive tertiary veins, accounts for the adaptive signifi cance of lobed leaves, predicting their occurrence in foliage that is thin in cross section and eff ectively broad (i.e., with substantial widths of leaves, lobes, or leafl ets), which matches the distribution of lobed leaves primarily in temperate deciduous forests and in the short-lived leaves of rapidly growing vines and early-successional trees of the lowland tropics ( Givnish, 1979 ).…”

“…Short stature plus thick, evergreen leaves should favor spinose leaf margins. rates of fl ow all the way to the hydraulically vulnerable areas nearest the leaf margin ( Roth et al, 1995 ). Th icker leaves should provide greater extraxylary conductance and be associated with lower photosynthetic rates, longer lifetimes, and lower transpiration rates, and thus permit looping connections between the secondary veins in various forms of camptodromous venation; such connections could promote greater long-term safety of the leaf hydraulic network, and the major veins paralleling the leaf margin could be permitted when extraxylary conductance is high ( Fig.…”

Viewing leaf structure and evolution from a hydraulic perspective

“…Open dichotomous venation is not a complete solution to leaf water supply however, because vein density gradients in the leaf are inevitable, leading to nonhomogeneous water transport and leaf water potential during transpiration (cf. Roth et al 1995). The most common open dichotomous leaf vein systems today are seen in ferns, where higher order veins are typically parallel at the leaf margin.…”