Ecological drivers and phylogenetic patterns of leaf minimum conductance variability in vascular plants

Stomatal closure prevents significant water losses during drought events. Yet, leaves are not perfectly hermetic and dehydration ensues through residual water losses, known as minimum conductance (g_min), which is highly relevant since it informs on the water depletion dynamics under stress. We measured g_min on 101 species spanning phylogenetic and ecological diversities, from ferns to flowering plants. Sampling also included different growth forms and life cycles from annual herbs to longevous trees. We used stomatal measurements to estimate operational (g_{th op}) and maximum (g_{th max}) conductances. Minimum water conductance is highly variable across species, and g_min shows a weak phylogenetic signal across vascular plants. Annual herbaceous plants have greater water loss than woody plants, and deciduous species showed higher g_min rates than evergreen species. Relationships of g_min with g_{th op} and g_{th max} were weak, revealing the lack of a clear tradeoff between maximum potential conductance efficiency and water retention. We found reduced water expenses in species occupying hotter and more seasonal environments. This study integrates g_min in leaf economics, where long-lived leaves show higher capabilities to retain water under stress. We provide important information in evolutionary physiology to understand the water loss dynamics under drought stress across clades of vascular plants.