Developmentally-based scaling of leaf venation architecture with leaf size explains global ecological patterns

Background/Question/Methods

Both leaf size and leaf venation show remarkable diversity across species of dicotyledons, and have recently been shown to be key determinants of plant adaptation to climate and of the dominant vegetation type in ecosystems past and present. However, little is known of the underlying bases for species differences in leaf venation architecture. Linkages of leaf vasculature with leaf size across species would have far-reaching implications for biogeography, evolution and global ecology. Based on detailed information of leaf and vein development and anatomy, we predicted fundamental global scaling of critical venation architecture traits with leaf size, which would be reinforced by selection based on function. Larger leaves should have larger-diameter major veins but lower major vein lengths per leaf area, with steeper trends for earlier-developing vein branching orders, but, in contrast, minor vein traits should be independent of leaf size. 

Results/Conclusions

Our quantitative scaling predictions were strongly supported across a new dataset for 485 globally distributed species. These scaling trends provide explanations for processes at a wide range of scales: the global biogeographic trend for smaller leaves in drier areas, the greater construction cost and lower photosynthetic return of larger leaves, and the ability of angiosperms to develop larger and more densely vascularized lamina to outcompete earlier-evolved plant lineages. These relationships can further be applied to estimate intact leaf size from fragments, to improve estimation of past climate and biodiversity from fossil remains.