Ecophysiological Traits May Explain the Abundance of Climbing Plant Species across the Light Gradient in a Temperate Rainforest Ernesto Gianoli 1,2,3 *, Alfredo Saldan ˜a 2 , Mylthon Jime ´ nez-Castillo 4 1 Departamento de Biologı ´a, Universidad de La Serena, La Serena, Chile, 2 Departamento de Bota ´nica, Universidad de Concepcio ´ n, Concepcio ´ n, Chile, 3 Center for Advanced Studies in Ecology and Biodiversity, Pontificia Universidad Cato ´ lica de Chile, Santiago, Chile, 4 Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile, Valdivia, Chile Abstract Climbing plants are a key component of rainforests, but mechanistic approaches to their distribution and abundance are scarce. In a southern temperate rainforest, we addressed whether the dominance of climbing plants across light environments is associated with the expression of ecophysiological traits. In mature forest and canopy gaps, we measured leaf size, specific leaf area, photosynthetic rate, and dark respiration in six of the most abundant woody vines. Mean values of traits and their phenotypic change (%) between mature forest and canopy gaps were predictor variables. Leaf size and specific leaf area were not significantly associated with climbing plant dominance. Variation in gas-exchange traits between mature forest and canopy gaps explained, at least partly, the dominance of climbers in this forest. A greater increase in photosynthetic rate and a lower increase in dark respiration rate when canopy openings occur were related to the success of climbing plant species. Dominant climbers showed a strategy of maximizing exploitation of resource availability but minimizing metabolic costs. Results may reflect phenotypic plasticity or genetic differentiation in ecophysiological traits between light environments. It is suggested that the dominant climbers in this temperate rainforest would be able to cope with forest clearings due to human activities. Citation: Gianoli E, Saldan ˜ a A, Jime ´nez-Castillo M (2012) Ecophysiological Traits May Explain the Abundance of Climbing Plant Species across the Light Gradient in a Temperate Rainforest. PLoS ONE 7(6): e38831. doi:10.1371/journal.pone.0038831 Editor: Minna-Maarit Kyto ¨ viita, Jyva ¨skyla ¨ University, Finland Received December 29, 2011; Accepted May 15, 2012; Published June 7, 2012 Copyright: ß 2012 Gianoli et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was funded by FONDECYT-Chile (Fondo Nacional de Desarrollo Cientı ´fico y Tecnolo ´ gico) grant number 1070503. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: egianoli@userena.cl Introduction Rainforests are heterogeneous ecosystems in terms of light availability [1,2] and show as a distinctive feature a considerable abundance of climbing plants [3–9]. This suggests that climbing plants, as a group, should be able to thrive under a range of light intensities. The relationship between light availability and climbing plant density has been evaluated in several rainforests worldwide (references in [4,9]). Overall, it seems that climbing plants show similar abundances across forest light gradients. Certainly, not all climbing plant species exhibit an even density throughout canopy gaps, secondary forest and mature forest; some species behave as light-demanding pioneers and some proliferate in the shaded understory of mature forests [3,4,9,10]. Functional explanations for the distribution of tree species with regard to light availability are widely available in the literature (reviewed in [11]), while there is little research on mechanistic explanations for distribution patterns of climbing plants across the light gradient. There is evidence of a relationship between the species’ climbing mechanism and both photosynthetic acclimation and abundance in contrasting light environments [12–14]. A field study recently reported that the dominance of climbing plant species in a shaded forest understory was positively related to light- interception efficiency and inversely related to potential carbon gain [15]. To our knowledge, no research has attempted to link the distribution and abundance of climbing plant species in contrast- ing light environments with the expression of ecophysiological traits related to light exploitation. This research question is of interest from a basic perspective, i.e., Do climbing plants show strategies of adaptation to light heterogeneity similar to those exhibited by trees?, considering that vines may account for 40% of species diversity in tropical forests [4], are present in more than 130 plant families [16], and the climbing habit is associated with increased diversification in plant lineages [17]. This question is also of interest to estimate the response of a key component of rainforest communities to changes in climate or land-use [8,18,19], considering evidence that woody climbers are increasing in dominance, relative to trees, in several forests worldwide [20– 23]. Here, we report results of a field study in a temperate rainforest showing a significant association between the domi- nance of climbing plant species across light environments and changes in ecophysiological traits between forest understory and canopy gaps. Materials and Methods The study was carried out in a temperate evergreen rainforest in Anticura, Southern Chile (40u399S, 72u119W; site and community details described in [9]). A research permit to conduct field work in Anticura, which is located within Puyehue National Park, was PLoS ONE | www.plosone.org 1 June 2012 | Volume 7 | Issue 6 | e38831