Waking up to respiration: leaf respiration in the light alters our interpretation of ecosystem carbon fluxes

In plants, respiration is usually inhibited in the light compared to the dark. Measuring respiration in the light is particularly difficult, because photosynthesis and photorespiration are occurring as well. Understanding how light respiration changes with temperature is crucial for predicting how ecosystem-level CO2 exchange will respond to climate change, which can feed back and amplify or dampen climate change depending on whether ecosystems take up less or more carbon as climate changes.

Red Oak Foliage
Red Oak foliage during autumn. Image: Famartin / Wikipedia

Recently in Tree Physiology, Mary Heskel and Jianwu Tang sought to understand how light respiration could affect ecosystem level carbon exchange. They measured respiration in the dark and light in oak trees (Quercus rubra) across the growing season and modelled the effects of light respiration on ecosystem-level CO2 exchange. They found that in general, respiration was suppressed in the light but that the level of suppression varied by season. At the ecosystem scale, it reduced predictions of ecosystem carbon loss by 8 or 13% across the growing season depending on whether they assumed that the suppression of light respiration varied seasonally or was constant.

What does this mean? It means that current models of ecosystem-scale CO2 exchange could be overestimating the amount of carbon lost to respiration if they assume that respiration is suppressed by light by a constant fraction. This translates into an underestimation of the ability of ecosystems to take up carbon from the atmosphere under current temperatures. Depending on the temperature response of light respiration, it is possible that ecosystems may have a greater capacity to dampen the effects of climate change in the future than is currently thought. However, there are myriad other factors beyond temperature that can affect ecosystem-scale carbon exchange, and more research is needed to understand how these factors can interact and affect light respiration.

Reference List

Heskel, M. A., & Tang, J. (2018). Environmental controls on light inhibition of respiration and leaf and canopy daytime carbon exchange in a temperate deciduous forest. Tree Physiology. https://doi.org/10.1093/treephys/tpy103