No evidence of canopy-scale leaf thermoregulation to cool leaves below air temperature across a range of forest ecosystems

Understanding and predicting the relationship between leaf temperature ( ) and air temperature ( ) is essential for projecting responses to a warming climate, as studies suggest that many forests are near thermal thresholds for carbon uptake. Based on leaf measurements, the limited leaf homeothermy...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2022-09, Vol.119 (38), p.e2205682119
Main Authors: Still, Christopher J, Page, Gerald, Rastogi, Bharat, Griffith, Daniel M, Aubrecht, Donald M, Kim, Youngil, Burns, Sean P, Hanson, Chad V, Kwon, Hyojung, Hawkins, Linnia, Meinzer, Frederick C, Sevanto, Sanna, Roberts, Dar, Goulden, Mike, Pau, Stephanie, Detto, Matteo, Helliker, Brent, Richardson, Andrew D
Format: Article
Language:English
Subjects:
Air temperature
BASIC BIOLOGICAL SCIENCES
Biological Sciences
Canopies
canopy temperature
Carbon
Carbon - metabolism
Carbon Cycle
Climate
Climate change
Energy balance
Forest ecosystems
Forests
functional traits
Global warming
Growing season
Health risks
High temperature
homeothermy
Hypotheses
leaf temperature
leaf traits
Leaves
Mortality risk
Photosynthesis
Physical Sciences
Plant Leaves - anatomy & histology
Plant Leaves - metabolism
Temperature
Terrestrial ecosystems
Thermal imaging
Thermoregulation
Thermoregulatory behavior
Thresholds
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Summary:Understanding and predicting the relationship between leaf temperature ( ) and air temperature ( ) is essential for projecting responses to a warming climate, as studies suggest that many forests are near thermal thresholds for carbon uptake. Based on leaf measurements, the limited leaf homeothermy hypothesis argues that daytime is maintained near photosynthetic temperature optima and below damaging temperature thresholds. Specifically, leaves should cool below at higher temperatures (i.e., > ∼25-30°C) leading to slopes 1 and hysteretic behavior. We find that the majority of ecosystem photosynthesis occurs when canopy leaves are warmer than air. Using energy balance and physiological modeling, we show that key leaf traits influence leaf-air coupling and ultimately the / relationship. Canopy structure also plays an important role in dynamics. Future climate warming is likely to lead to even greater , with attendant impacts on forest carbon cycling and mortality risk.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.2205682119