Leaf Gas Exchange in Canopy Species of a Venezuelan Cloud Forest

Abstract

Tropical cloud forests are considered humid ecosystems with frequent cloud cover down to the ground surface. However, seasonal variation in precipitation may induce short-term water stress. For canopy leaves, this water stress may also be a consequence of large atmospheric vapor pressure deficits. The objective of this work was to study five canopy cloud forest species to determine if there are restrictions to leaf gas exchange as a consequence of seasonality in precipitation and to daily water deficit due to air evaporative demand mainly during maximum incoming radiation hours. Seasonal daily courses of microclimatic variables (air temperature, relative humidity, photosynthetic photon flux density) and plant responses (leaf water potential, stomatal conductance, CO 2 assimilation rates, leaf nitrogen concentration) were measured at 2400 m asl in Monterrey, an intermontane valley of the Venezuelan Andes. A gradient in terms of responses to water stress conditions was observed between the species, with Clusia multiflora (a 46% reduction in stomatal conductance between seasons) as the most affected and Miconia resimoides (increased stomatal conductance) responding more favorably to slight water stress conditions. If we consider the limitations of water stress and/or light conditions on CO 2 assimilation we may arrange the species into those in which water stress conditions have a greater impact on leaf carbon gain, those where light conditions are determinant and one in which both water stress and light conditions may affect leaf carbon assimilation.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.

Drought resistance increases from the individual to the ecosystem level in highly diverse neotropical rain forest: a meta-analysis of leaf, tree and ecosystem responses to drought

“…Following the definition of Martinez-Vilalta et al (2014): the water potential gradient generally increases with a decline in pre-dawn in response to seasonal and episodic drought (Figure 3 & 4, Figure S2). The observed insensitivity of stomatal conductance to VPD in high wood density trees has been reported previously for lowland rainforest species (Bonal et al, 2000a;Domingues et al, 2014;Granier et al, 1992;Huc et al, 1994) and for tree species of tropical montane cloud forest (Rada et al, 2009). Stomatal insensitivity to VPD is a possible adaptation to surviving in a humid and deeply shaded understory, as the CO 2 concentration inside the leaf is kept high to maximize photosynthesis during brief moments of high irradiance, known as sun flecks (Domingues et al, 2014;Pons et al, 2005;Tinoco-Ojanguren and Pearcy, 1992).…”

Height-diameter allometry of tropical forest trees

“…Following the arguments above, one possibility accounting for this is adverse water relations at higher elevation, for example, due to an increased viscosity of water at lower temperatures (Roderick and Berry, 2001). But there is little to suggest that montane trees are any different from lowland trees in terms of hydraulic construction (Coomes et al, 2007) and, if anything, the available evidence suggests lower likelihood of soil water deficits adversely affecting the function of higher altitude trees (Cavelier, 1990;Zotz et al, 1998;Rada et al, 2009).…”

Height-diameter allometry of tropical forest trees

“…Following the arguments above, one possibility accounting for this is adverse water relations at higher elevation, for example, due to an increased viscosity of water at lower temperatures (Roderick and Berry, 2001). But there is little to suggest that montane trees are any different from lowland trees in terms of hydraulic construction (Coomes et al, 2007) and, if anything, the available evidence suggests lower likelihood of soil water deficits adversely affecting the function of higher altitude trees (Cavelier, 1990;Zotz et al, 1998;Rada et al, 2009).…”