Document: REB-3-29-23

Leaf-level and whole-plant assimilation as predictors of tree seedling growth across a broad light gradient.

MONTGOMERY, R.A.* ^1,2

University of Connecicut, Storrs, CT, USA ¹
University of Wisconsin, Madison, WI, USA ²

Abstract:
I explored leaf-level photosynthetic capacity, whole-plant assimilation rates and whole-plant carbon gain as predictors of biomass growth in tree seedlings growing across a broad light gradient in NE Costa Rica. Seedlings of Dipteryx panamensis, Virola koschnyii, and Brosimum alicastrum were transplanted along transects spanning a secondary forest-pasture edge at La Selva Biological Station. Light availability ranged from 80% to <1% diffuse transmittance. Estimates of whole-plant assimilation rates were generated using the three-dimensional crown architecture model, YPLANT. Leaf-level photosynthetic capacity was positively related to final biomass of seedlings of Dipteryx (R²=0.34, p=0.05) and Virola (R²=0.66, p=0.003) but not Brosimum (R²=-0.14, p=0.87). In contrast, whole-plant assimilation rates were unrelated to final biomass in all species (R²=0.19, 0.15, and 0.13 for Dipteryx, Virola, and Brosimum respectively). Estimated whole-plant carbon gain, which adjusts whole-plant assimilation rate by seedling leaf area, was the strongest predictor of final seedling size. Increases in estimated daily carbon gain were positively related to final seedling biomass in all three species (Dipteryx, R²=0.90, p<0.0001; Virola, R²=0.89, p<0.0001; Brosimum, R²=0.48, p=0.0004). Measures of whole-plant carbon gain combine leaf-level acclimation, plant architecture, leaf area and plant light environment and represent an integrative measure of physiological and morphological performance. These data show that scaling leaf-level physiology to the same level of organization (whole-plant) as growth results in a clearer coupling betweens seedling ecophysiology and growth.

Keywords: photosynthesis, carbon gain, growth, light relations, Costa Rica, scaling, YPLANT

This abstract is being presented at: 2:15 PM in session:
Oral Session #10: Light Relations in Plants.