Stomatal Traits are Evolutionarily Associated with Vein Density in Basal Angiosperms

Plant leaves reach water balance by evaporative water loss through stomata and water supply from leaf veins. However,it is still unclear whether water supply and transpiration demand maintained balance during the evolution of basal angiosperms. In the present study,we measured stomatal density,stomatal length,vein density and leaf thickness from 11 basal angiosperm species and applied phylogenetically independent contrasts,combined with phylogenetic trees,to detect correlated-evolution between traits. Our results showed that along the evolutionary direction,stomatal density and vein density increased gradually while stomatal length and leaf thickness expressed a declining trend; whether phylogeny was considered or not,stomatal density was positively correlated with vein density,indicating their correlated-evolution,and supporting the hypothesis that leaf water balance existed in basal angiosperms; leaf thickness was correlated significantly with both stomatal traits and vein density; however,after removing the phylogenetic effect,these correlations disappeared,indicating non-correlated evolution between these traits. The results of the present study revealed that the maintenance of the balance between water demand and supply,and even CO₂ supply,drove the evolution of leaf structure and function in basal angiosperms.