In situ temperature response of photosynthesis of 42 tree and liana species in the canopy of two Panamanian lowland tropical forests with contrasting rainfall regimes

Abstract

Tropical forests contribute significantly to the global carbon cycle, but little is known about the temperature response of photosynthetic carbon uptake in tropical species, and how this varies within and across forests. We determined in situ photosynthetic temperature-response curves for upper canopy leaves of 42 tree and liana species from two tropical forests in Panama with contrasting rainfall regimes. On the basis of seedling studies, we hypothesized that species with high photosynthetic capacity - light-demanding, fast-growing species - would have a higher temperature optimum of photosynthesis (T_Opt ) than species with low photosynthetic capacity - shade-tolerant, slow-growing species - and that, therefore, T_Opt would scale with the position of a species on the slow-fast continuum of plant functional traits. T_Opt was remarkably similar across species, regardless of their photosynthetic capacity and other plant functional traits. Community-average T_Opt was almost identical to mean maximum daytime temperature, which was higher in the dry forest. Photosynthesis above T_Opt appeared to be more strongly limited by stomatal conductance in the dry forest than in the wet forest. The observation that all species in a community shared similar T_Opt values suggests that photosynthetic performance is optimized under current temperature regimes. These results should facilitate the scaling up of photosynthesis in relation to temperature from leaf to stand level in species-rich tropical forests.

Keywords: climate change; leaf economics spectrum; lianas; photosynthetic temperature response; plant functional traits; stomatal conductance; thermal acclimation; tropical forest.