What is it about?

Leaf temperature has long been recognized as important for plant function, and climate warming may lead to outsized impacts on leaf temperature and function. This includes carbon assimilation, as numerous studies suggest that a variety of ecosystems are operating at or near thermal thresholds. However, sustained, high-frequency measurements of canopy-scale leaf temperature across a range of ecosystems and conditions are rare. We show that daytime canopy leaf temperatures do not cool below air as predicted by the leaf homeothermy hypothesis.

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Why is it important?

Leaves are typically warmer than air and the magnitude of this departure varies with leaf size and canopy structure. Almost all ecosystem photosynthesis occurs when leaf temperature exceeds air temperature. Future warming is unlikely to be mitigated by leaf cooling in forests.


While leaves can certainly cool below air temperature during the hottest part of the day in some ecosystems, we find this does not occur commonly in a range of forests. Canopy leaves warm at the same or higher rate as air and thus are highly susceptible to climate warming.

Christopher Still

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This page is a summary of: No evidence of canopy-scale leaf thermoregulation to cool leaves below air temperature across a range of forest ecosystems, Proceedings of the National Academy of Sciences, September 2022, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2205682119.
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