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?

Abstract

The crown architectures of 11 Psychotria species native to Barro Colorado Island, Panama were reconstructed from field measurements of leaf and branch geometry with the three-dimensional simulation model Yplant. The objective was to assess the role of species differences in architecture in light capture and carbon gain in their natural understory environment. When species were grouped according to their putative light environment preference, the shade tolerant species were found to have a small but significantly higher efficiency of light capture for both diffuse and direct light as compared to the light demanding species. Within each grouping, however, there were few significant differences in light capture efficiency among species. The lower efficiencies of light demanding species was due to slightly higher self-shading and slightly lower angular efficiencies. Simulations of whole plant assimilation showed that light demanding species had greater daily assimilation in both direct and diffuse light due to the significantly greater light availability in the sites where light demanding species were found, as compared to those where shade tolerant species occurred. Among light demanding species, the above ground relative growth rate measured over a 1-year period by applying allometric equations for mass versus linear dimensions, was positively correlated with diffuse PFD and with mean daily assimilation estimated from Y-plant. For the shade tolerant plants, there was no significant correlation between RGR and mean daily assimilation or with any measure of light availability, probably because they occurred over a much narrower range of light environments. Overall, the results reveal a strong convergence in light capture efficiencies among the Psychotria species at lower values than previously observed in understory plants using similar approaches. Constraints imposed by other crown functions such as hydraulics and biomechanical support may place upper limits on light capture efficiency.

Crown architecture and leaf habit are associated with intrinsically different light-harvesting efficiencies inQuercusseedlings from contrasting environments

“…Similarly, species mean leaf size and self-shading explained most of the variance in light capture of many perennial plants coexisting in Australia temperate forests [11]. Our findings are consistent with results from simulation studies based on virtual plants which found that the higher self-shading was due both to crowding of leaves close to each other and to proximity of leaves to the stem [11,25,33,45,47,50].…”

“…The connections between structure and function of plant developmental patterns in relation to light harvesting have received renewed attention during the last years [33]. However, most studies have focused on modeling instead of performing direct measurements of the light really harvested by the plant crown and by the individual leaves within the foliage [27,30,35].…”

“…1) and to calculate light harvesting efficiency by actual plants at a given latitude and date. Y-plant has since then been successfully used in a number of functional and ecophysiological studies of plants [11,33,34,45].…”

Leaf size and leaf display of thirty-eight tropical tree species

“…Leaf display and light capture depend on intra-and interspeciWc responses to light, and the size of the leaves (Falster and Westoby 2003;Pearcy et al 2004Pearcy et al , 2005. Nearly all our knowledge on intraspeciWc metamer responses to light comes from herbaceous (clonal) plants that vary internode length to forage for resources and explore resource-rich patches (Hutchings and de Kroon 1994).…”

The crown efficiency of Parana-Pine

“…The growth depends on the light quantity absorbed in leaves, also on the efficiency of the conversion of light absorbed in biomass and allocation of photoassimilates in tissues . The capture of light by a plant depends on the amount of radiation and the architectural arrangement of leaves within the crown, on a direct leaf orientation to the light sources and on the degree of shading resulting from the overlap of the leaf in a plane orthogonal to the light source (Pearcy et al, 2004).…”