Functional variation of leaf succulence in a cold rainforest epiphyte

Abstract

Background and aims - Succulence, a common attribute of foras in dry regions and of species living in microenvironments with transient water shortage, has been typically viewed as an adaptive plant feature for surviving in (semi-)arid conditions. The existence of leaf succulence in a temperate cold rainforest challenges the view of its adaptive value. We studied leaf functional variation in Sarmienta repens Ruiz & Pav. (Gesneriaceae), an epiphyte living in the Valdivian forest of southern Chile.Material and methods - We measured leaf thickness, absolute leaf water content, specifc leaf area and leaf anatomy (epidermis, palisade parenchyma, and spongy parenchyma) in two distinct light micro-environments: shaded understory versus border of canopy gaps. We also characterized micro-environmental conditions in terms of light availability, temperature and water evaporation. Key results - We show that leaves from sun conditions, the environment with higher water demand, have lower SLA (specifc leaf area), thicker epidermis and store more water due to a thicker spongy parenchyma, than leaves from shade conditions.Conclusions - We found high phenotypic variation in S. repens at intraspecifc level in response to contrasting environmental conditions. This variation refects a two-fold strategy common in epiphytes: increase water storage and reduce water loss. Furthermore, it suggests that leaf succulence has an adaptive value even in a temperate cold rainforest. We discuss that the occurrence of succulence on a cold rainforest might be explained by a combination of ecological, biogeographic and phylogenetic factors. © 2013 National Botanic Garden of Belgium and Royal Botanical Society of Belgium.