Experimental warming across a tropical forest canopy height gradient reveals minimal photosynthetic and respiratory acclimation

Abstract

Tropical forest canopies cycle vast amounts of carbon, yet we still have a limited understanding of how these critical ecosystems will respond to climate warming. We implemented in situ leaf-level + 3°C experimental warming from the understory to the upper canopy of two Puerto Rican tropical tree species, Guarea guidoniaand Ocotea sintenisii. After approximately 1 month of continuous warming, we assessed adjustments in photosynthesis, chlorophyll fluorescence, stomatal conductance, leaf traits and foliar respiration. Warming did not alter net photosynthetic temperature response for either species; however, the optimum temperature of Ocoteaunderstory leaf photosynthetic electron transport shifted upward. There was no Ocotearespiratory treatment effect, while Guarearespiratory temperature sensitivity (Q₁₀) was down-regulated in heated leaves. The optimum temperatures for photosynthesis (T_opt) decreased 3-5°C from understory to the highest canopy position, perhaps due to upper canopy stomatal conductance limitations. Guareaupper canopy T_optwas similar to the mean daytime temperatures, while Ocoteacanopy leaves often operated above T_opt. With minimal acclimation to warmer temperatures in the upper canopy, further warming could put these forests at risk of reduced CO₂uptake, which could weaken the overall carbon sink strength of this tropical forest.

Citation

Carter, Kelsey R.; Wood, Tana E.; Reed, Sasha C.; Butts, Kaylie M.; Cavaleri, Molly A. 2021. Experimental warming across a tropical forest canopy height gradient reveals minimal photosynthetic and respiratory acclimation. Plant, Cell & Environment. 44(9): 2879-2897. https://doi.org/10.1111/pce.14134.