Convergence in light capture efficiencies among tropical forest understory plants with contrasting crown architectures: a case of morphological compensation

Abstract

Leaf and crown characteristics were examined for 24 tree and herbaceous species of contrasting architectures from the understory of a lowland rainforest. Light-capture efficiency was estimated for the crowns of the different species with a three-dimensional geometric modeling program. Causal relationships among traits affecting light absorption at two hierarchical levels (leaf and whole crown) were quantified using path analysis. Light-capture and foliage display efficiency were found to be very similar among the 24 species studied, with most converging on a narrow range of light absorption efficiencies (ratio of absorbed vs. available light of 0.60-0.75). Exceptionally low values were found for the climber vines and, to a lesser extent, for the Bromeliad Aechmea magdalenae. Differences in photosynthetic photon flux density (PFD) absorbed per unit leaf area by individual plants were mostly determined by site to site variation in PFD and not by the differences in crown architecture among individuals or species. Leaf angle, and to a lesser extent also supporting biomass, specific leaf area, and internode length, had a significant effect on foliage display efficiency. Potential constraints on light capture such as the phyllotactic pattern were generally offset by other compensatory adjustments of crown structure such as internode length, arching stems, and plagiotropy. The variety of shoot morphologies capable of efficiently capturing light in tropical forest understories is greater than initially thought, extending over species with very different phyllotactic patterns, crown architectures, leaf sizes, and morphologies.

A functional analysis of the crown architecture of tropical forest Psychotria species: do species vary in light capture efficiency and consequently in carbon gain and growth?

“…This convergence occurs around values of £"« for the Psychotria species are certainly lower than those determined for a majority of other shade tolerant species surveyed on BCI by Valladares et al (2002). Thus, it is somewhat paradoxical that on one hand a higher Ea should lead to higher assimilation, yet the Psychotria with their lower Ea are the single most abundant genus making up about 5% of the shade tolerant stems on BCI.…”

“…Notwithstanding the substantial variation in leaf size, branching patterns and general appearance of the crowns of the Psychotria species, the most remarkable features of the results are the relatively small variations in measures of light capture efficiency among species and, overall, the rather low values of Ea- Valladares et al (2002) surveyed 24 understorey species covering a wide range of taxa and growth forms occurring in the shade tolerant on BCI and found that there was substantial convergence in Ea and DE. However, excluding some very low Ea values determined for climbers, Ea ranged from 0.3 to 0.83 with 50% of the species sampled having ¿"^'s >0.72.…”

“…Most early quantitative studies treated crowns as two dimensional arrays of leaves with light being received only Irom above, but the development of three-dimensional simulation models (Takenaka 1994;Pearcy and Yang 1996) has allowed for a more realistic evaluation of light capture by plant crowns in complex light environments. Valladares et al (2002) examined the relationships between leaf and crown characteristics and light capture efficiency for 24 understory species Irom a tropical forest on Barro Colorado Island, Panama using the threedimensional crown architecture model, Y-plant (Pearcy and Yang 1996). The species studied represented a wide range of taxa, life forms and crown architectures and the objective of the study was to determine the fiinctional correlates between light capture efficiency and leaf and crown characteristics.…”

Links between tree structure and functional leaf traits in the tropical forest tree Dicorynia guianensis Amshoff (Caesalpiniaceae)

“…D. guianensis, like numerous other tropical species [67,86], increases its leaf life-span in the understorey (mean leaf life span of saplings in understorey ranging from 3 to 4 years [5,74] vs. 18 months in clearings [5]. This results in a greater biomass accumulation and provides a means to compensate for the leaf construction costs over time [6,73,83], and to enable the construction of an efficient foliar display for light interception [30,68,87]. Because leaf size also increases with increasing tree age in D. guianenis (data not shown) such adjustments require an increasing assimilate investment in the leaf area formation during tree development.…”

Leaf Morphological Plasticity of Tree Species from Two Developmental Stages in Araucaria Forest

“…The results supported only partially the morphological premises described for the understory plants, including thin leaves with lower dry matter and stomata density, higher leaf area and specific leaf area, when compared to canopy leaves or the plants with higher light availability (Givnish 1988;Popma and Bongers 1988;Valladares et al 2002;Johnson et al 2005;Rozendaal et al 2006;Kitajima and Poorter 2010). The dry matter did not follow the expected pattern, because young stage leaves presented higher dry matter than the adult stage leaves, except L. divaricata.…”