Carbon Allocation and Water Relations of Lianas Versus Trees

Abstract

Despite lianas being fundamental components of tropical and subtropical forest ecosystems throughout the world, the physiological characteristics of this growth form are not well known. Different behaviors at the seedling stage were until recently largely unnoticed. In one extreme of a continuum of adaptive traits, freestanding liana seedlings invest a large proportion of biomass in self-support tissue while on the other extreme support-seeker seedlings invest more resources in rapid elongation of slender stems with an efficient hydraulic conductive system. Adult lianas often have lower wood density and higher specific leaf area than trees and have most of their leaves deployed at the top of the canopy, experiencing high irradiance and transpirational demands, which requires effective regulation of water loss to avoid desiccation. Recent studies show that lianas have faster stomatal responses to increasing vapor pressure deficit (VPD) and exhibit stronger partial stomatal closure compared to trees. Strong stomatal control and efficient water transport help lianas maintain leaf water potential (Ψleaf) within a safe hydraulic range to avoid xylem dysfunction despite their low stem water storage capacity, which is achieved at a minimum cost in terms of carbon assimilation. Liana colonization of tree crowns can significantly reduce tree growth and transpiration with consequences for carbon and water economy at individual tree and ecosystem levels.