No evidence of homeostatic regulation of leaf temperature in Eucalyptus parramattensis trees: integration of CO2 flux and oxygen isotope methodologies

John E. Drake, Richard Harwood, Angelica Vårhammar, Margaret M. Barbour, Peter B. Reich, Craig V.M. Barton, Mark G. Tjoelker

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Thermoregulation of leaf temperature (Tleaf) may foster metabolic homeostasis in plants, but the degree to which Tleaf is moderated, and under what environmental contexts, is a topic of debate. Isotopic studies inferred the temperature of photosynthetic carbon assimilation to be a constant value of c. 20°C; by contrast, leaf biophysical theory suggests a strong dependence of Tleaf on environmental drivers. Can this apparent disparity be reconciled? We continuously measured Tleaf and whole-crown net CO2 uptake for Eucalyptus parramattensis trees growing in field conditions in whole-tree chambers under ambient and +3°C warming conditions, and calculated assimilation-weighted leaf temperature (TL-AW) across 265 d, varying in air temperature (Tair) from −1 to 45°C. We compared these data to TL-AW derived from wood cellulose δ18O. Tleaf exhibited substantial variation driven by Tair, light intensity, and vapor pressure deficit, and Tleaf was strongly linearly correlated with Tair with a slope of c. 1.0. TL-AW values calculated from cellulose δ18O vs crown fluxes were remarkably consistent; both varied seasonally and in response to the warming treatment, tracking variation in Tair. The leaves studied here were nearly poikilothermic, with no evidence of thermoregulation of Tleaf towards a homeostatic value. Importantly, this work supports the use of cellulose δ18O to infer TL-AW, but does not support the concept of strong homeothermic regulation of Tleaf.

Original languageEnglish (US)
Pages (from-to)1511-1523
Number of pages13
JournalNew Phytologist
Volume228
Issue number5
DOIs
StatePublished - Dec 1 2020

Bibliographical note

Funding Information:
We thank Burhan Amiji (Western Sydney University) for maintaining the site and for his excellent research support. We thank Kristine Crous and David Ellsworth for the use of some leaf thermocouples and gallium‐arsenide photodiodes, and Wenbo Yang for stable isotope mass spectrometry. This experiment was made possible through a collaboration with Sune Linder and the Swedish University of Agricultural Sciences, who designed, built, and generously provided the whole‐tree chambers. This work was improved by seven rigorous anonymous reviews. This research was supported by the Australian Research Council (Discovery, DP140103415 to MGT, JED and PBR; and DP171014276 to MMB), the Hawkesbury Institute for the Environment, and Western Sydney University.

Funding Information:
We thank Burhan Amiji (Western Sydney University) for maintaining the site and for his excellent research support. We thank Kristine Crous and David Ellsworth for the use of some leaf thermocouples and gallium-arsenide photodiodes, and Wenbo Yang for stable isotope mass spectrometry. This experiment was made possible through a collaboration with Sune Linder and the Swedish University of Agricultural Sciences, who designed, built, and generously provided the whole-tree chambers. This work was improved by seven rigorous anonymous reviews. This research was supported by the Australian Research Council (Discovery, DP140103415 to MGT, JED and PBR; and DP171014276 to MMB), the Hawkesbury Institute for the Environment, and Western Sydney University.

Publisher Copyright:
© 2020 The Authors. New Phytologist © 2020 New Phytologist Foundation

Keywords

  • Eucalyptus parramattensis
  • carbon cycle
  • climate warming
  • endothermy
  • photosynthesis
  • temperature regulation

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't

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