Leaf Venation Network

Spatial transportation networks are critical to multicellular terrestrial organisms, including animal circulatory systems, fungal mycelial networks, and plant vasculature. These networks represent evolved solutions to maximize functional benefits relative to some set of construction costs. Although the functions vary across these domains, all these networks can share similar features, e.g. the presence of hierarchical structure, fractal-like branching, and/or nested loops. There may be general principles that unify relationships between architecture and function in these networks. Extant theory has only been able to predict primarily branching networks, suggesting that more accurate rules remain discoverable. The goal of our research is to understand the rules that link network architecture to network function using leaf venation networks as a model system. Discovering these principles could advance fundamental theory for networks and physical transport, as well as provide insight into the selective forces and biophysical constraints that have led to the evolution of organisms with diverse network architectures.

Leaf architecture and functional traits for 122 species at the University of California at Berkeley botanical garden

We collected leaf venation architecture and functional traits for a phylogenetically diverse set of 122 plant species (including ferns, basal angiosperms, monocots, basal eudicots, asterids, and rosids) sampled from the living collections of the University of California Botanical Garden at Berkeley. The sampled species originated from all continents, except Antarctica, and are distributed in different growth forms (aquatic, herb, climbing, tree, shrub). Our functional dataset comprises 32 (mechanical, hydraulic, anatomical, physiological, economical, and chemical) traits and provides a complete description of the six main leaf functional axes (flow efficiency, damage resistance to drought, resistance to herbivory, resilience, mechanical support, and construction cost). The leaf venation architecture trait dataset comprises over 5 million vein segments extracted from high-resolution whole-leaf images and contains 58 single- and 22 multiscale-statistics describing how network architecture features vary across the entire venation network. Our high-dimensional architecture-functional paired trait dataset is suitable for (1) functional and architectural characterization of plant species; (2) identification of venation architecture-function trade-offs; (3) investigation of evolutionary trends in leaf venation networks, and (4) mechanistic modeling of leaf function.

[Data available at - COMING SOON!]

Leaf venation network architecture coordinates functional trade-offs across vein spatial scales: evidence for multiple alternative designs

We measured architecture and functional traits on 122 ferns and angiosperms species to: describe how trade-offs vary across phylogenetic groups and vein spatial scales (small, medium, large veins) and determine whether architecture traits at each scale have independent or integrated effects on each function. 

We found that generalized architecture-function trade-offs are weak. Architecture strongly predicts leaf support and damage resistance axes, but weakly predicts efficiency and resilience axes. Architecture traits at different spatial scales contribute to different functional axes, allowing plants to independently modulate different functions by varying network properties at each scale.

This independence of vein architecture traits within and across spatial scales may enable evolution of multiple alternative designs of leaf networks that achieve equivalent functions or trade-off among multiple functions. 

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Leaf conduits grow wider than thicker and are potentially vulnerable to implosion under drought

Xylem conduits have lignified walls to resist crushing pressures. The thicker the double-wall (T) relative to its maximum diameter (D), the greater the collapse/implosion resistance. Having xylem that is more resistant than necessary incurs high costs and reduced flow, while having xylem not resistant enough may lead to catastrophic collapse under drought. Despite the importance of xylem implosion safety in determining plant drought resistance, it is still unclear how leaves scale TxD to trade-off among implosion safety, flow efficiency, mechanical support, and construction cost. We measured T and D in over 7,000 leaf xylem conduits of 122 ferns and angiosperms species to investigate how the TxD scaling varies across species, clades, habitats, growth forms, and vein orders. Overall, leaf xylem conduits grow wider than thicker, potentially resulting in high flow efficiency and lower cost, but at the expense of high vulnerability to implosion. Conduits seem particularly vulnerable to implosion in monocots, aquatic species and in species from hydric habitats, as well as in major veins. The absence of strong trade-offs within the leaf functional traits examined suggests that implosion safety at the whole-leaf level cannot be easily predicted by the sum of the individual conduits’ resistance to collapse.

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Evolutionary trends in the leaf venation network architecture

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Simulations of leaf functioning using electronic circuits

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