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

C. J. Still; G. Page; B. Rastogi; D. M. Griffith; D. M. Aubrecht; Y. Kim; S. P. Burns; C. V. Hanson; H. Kwon; L. Hawkins; F. C. Meinzer; S. Sevanto; D. Roberts; M. Goulden; S. Pau; M. Detto; B. Helliker; A. D. Richardson; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

doi:10.1073/pnas.2205682119

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

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

C. J. Still, G. Page, B. Rastogi, D. M. Griffith, D. M. Aubrecht, Y. Kim, S. P. Burns, C. V. Hanson, H. Kwon, L. Hawkins, …

Proceedings of the National Academy of Sciences - PNAS, Vol.119(38), e2205682119

2022

DOI: https://doi.org/10.1073/pnas.2205682119

PMID: 36095211

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Abstract

Multidisciplinary Sciences

Science & Technology

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Understanding and predicting the relationship between leaf temperature (T-leaf) and air temperature (T-air) 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 Tleaf is maintained near photosynthetic temperature optima and below damaging temperature thresholds. Specifically, leaves should cool below Tair at higher temperatures (i.e., > similar to 25-30 degrees C) leading to slopes <1 in T-leaf /T-air relationships and substantial carbon uptake when leaves are cooler than air. This hypothesis implies that climate warming will be mitigated by a compensatory leaf cooling response. A key uncertainty is understanding whether such thermoregulatory behavior occurs in natural forest canopies. We present an unprecedented set of growing season canopy-level leaf temperature (Tcan) data measured with thermal imaging at multiple well-instrumented forest sites in North and Central America. Our data do not support the limited homeothermy hypothesis: canopy leaves are warmer than air during most of the day and only cool below air in mid to late afternoon, leading to Tcan/Tair 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 Tcan/Tair relationship. Canopy structure also plays an important role in Tcan dynamics. Future climate warming is likely to lead to even greater Tcan, with attendant impacts on forest carbon cycling and mortality risk.

Details

Title: No evidence of canopy-scale leaf thermoregulation to cool leaves below air temperature across a range of forest ecosystems
Authors/Creators: C. J. Still - Oregon State University
G. Page - Murdoch University, College of Environmental and Life Sciences
B. Rastogi - Cooperative Institute for Research in Environmental Sciences
D. M. Griffith - Oregon State University
D. M. Aubrecht - Northern Arizona University
Y. Kim - Canadian Armed Forces
S. P. Burns - University of Colorado Boulder
C. V. Hanson - Oregon State University
H. Kwon - Oregon State University
L. Hawkins - Oregon State University
F. C. Meinzer - US Forest Service
S. Sevanto - Los Alamos National Laboratory
D. Roberts - University of California, Santa Barbara
M. Goulden - Univ Calif Irvine, Dept Earth Syst Sci, Irvine, CA 92697 USA
S. Pau - Florida State University
M. Detto - Princeton University
B. Helliker - University of Pennsylvania
A. D. Richardson - Northern Arizona University
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Details: Proceedings of the National Academy of Sciences - PNAS, Vol.119(38), e2205682119
Publisher: Natl Acad Sciences
Number of pages: 8
Grant note: Los Alamos Center of Space and Earth Sciences USDA McIntire Stennis program EF 1241873; IOS 0950998; DEB 1237491; DEB 1832210; EF 1241616; EF 1702697 / NSF; National Science Foundation (NSF) Princeton's Carbon Mitigation Initiative 1241953 / National Science Foundation (NSF)
Identifiers: 991005550569207891
Murdoch Affiliation: School of Environmental and Conservation Sciences; College of Environmental and Life Sciences
Language: English
Resource Type: Journal article

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Collaboration types: Domestic collaboration; International collaboration
Citation topics: 3 Agriculture, Environment & Ecology; 3.40 Forestry; 3.40.55 Forest Dynamics
Web Of Science research areas: Plant Sciences
ESI research areas: Plant & Animal Science