The Science

Leaf respiration contributes an estimated 50% of total plant respiration. But with few observations in the tropics, there is high uncertainty in the amount of leaf respiration, how it varies across common tree species as a function of height, and how light influences the respiratory process. This study shows that canopy position has an important influence on leaf respiratory rates and the degree of light suppression in tropical forests of the Amazon.

The Impact

This study provides a better understanding of how leaf functional traits and their connections with the carbon cycle and energy metabolism vary in different environmental conditions. These findings highlight the importance of representing light suppression of leaf respiration in dynamic vegetation models aimed at predicting the future of tropical forests under climate change.

Summary

Leaf respiration is a major contributor to plant respiration but is poorly characterized in diverse tropical ecosystems. Light can inhibit this process, but little information is available about the degree to which light suppression impacts leaf respiration or how that impact varies within a tropical forest canopy. Due to the Amazon rainforest’s importance in the global climate context, this study quantified rates of daytime and dark leaf respiration and investigated potential influences of canopy position on variation in leaf respiration rates and light suppression. Measurements were collected from 26 tree individuals of different species distributed in three different canopy positions: canopy, lower canopy, and understory. While rates of leaf respiration increased from the understory upward into the canopy, the influence of light suppression followed an opposite pattern. Canopy trees had significantly higher rates of R_dark and R_day than trees in the understory. However, the difference between R_dark and R_day (the light suppression of respiration) was greatest in the understory (68 ± 9%, 95% CI) decreasing in the lower canopy (49 ± 9%, 95% CI), and reaching the lowest values in the canopy (37 ± 10%, 95% CI). These findings highlight the importance of including representation of the light suppression of leaf respiration in terrestrial biosphere models, as well as accounting for vertical gradients within forest canopies and connections with functional traits for predicting tropical forest function.

Principal Investigator

Daisy Souza
National Institute of Amazonian Research (INPA)
daisysouza21@gmail.com

Co-Principal Investigator

Kolby Jardine
National Institute of Amazonian Research (INPA)
kjjardine@lbl.gov

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
brian.benscoter@science.doe.gov

Funding

This research is based upon work supported as part of the Next Generation Ecosystem Experiments–Tropics (NGEE–Tropics) as a part of work package 1.4 (Autotrophic respiration) funded by the Biological and Environmental Research (BER) Program’s Environmental System Science program within the U.S. Department of Energy’s (DOE) Office of Science. Additional funding for this research was provided by the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

References