Eco-Physiological Traits of Leaves from Basal Angiosperm Machilus Species with Localized and Widespread Distribution

Machilus species are basal angiosperms, which are mostly distributed in humid tropical and subtropical forest habitats, though a few species are widely distributed. In this study, we measured hydraulic-related traits of sapling leaves from 11 Machilus species, which included leaf mass per area, leaf density, stomatal density, vein density, leaf turgor loss point, and palisade and spongy tissue thickness. We found that, on average, Machilus species had lower vein density compared with that of other tropical and subtropical angiosperms, indicating this trait was strongly influenced by evolution. Leaf vein density was positively and significantly correlated with stomatal density and the ratio of palisade to spongy tissue thickness, indicating the balance between leaf water transpirational demand and supply. Compared with localized species, widespread species were more drought-tolerant and exhibited lower turgor loss point and higher leaf density. Turgor loss point was negatively and significantly correlated with maximum tree height across species, indicating that leaf drought resistance was controlled by genetics. Our study suggests that leaf hydraulic traits can be used to explain the geographical distribution of Machilus species.