Examining the evidence for decoupling between photosynthesis and transpiration during heat extremes
<p>Recent experimental evidence suggests that during heat extremes, wooded ecosystems may decouple photosynthesis and transpiration, reducing photosynthesis to near zero but increasing transpiration into the boundary layer. This feedback may act to dampen, rather than amplify, heat extremes in...
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doaj-8ee3aa2c6e1f4ff5b1d55ce805f7cdcb2020-11-24T23:06:44ZengCopernicus PublicationsBiogeosciences1726-41701726-41892019-02-011690391610.5194/bg-16-903-2019Examining the evidence for decoupling between photosynthesis and transpiration during heat extremesM. G. De Kauwe0M. G. De Kauwe1B. E. Medlyn2A. J. Pitman3A. J. Pitman4J. E. Drake5A. Ukkola6A. Ukkola7A. Griebel8E. Pendall9S. Prober10M. Roderick11M. Roderick12ARC Centre of Excellence for Climate Extremes, Sydney, NSW 2052, AustraliaClimate Change Research Centre, University of New South Wales, Sydney, NSW 2052, AustraliaHawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, AustraliaARC Centre of Excellence for Climate Extremes, Sydney, NSW 2052, AustraliaClimate Change Research Centre, University of New South Wales, Sydney, NSW 2052, AustraliaForest and Natural Resources Management, SUNY-ESF, Syracuse, NY, USAARC Centre of Excellence for Climate Extremes, Canberra, ACT 2601, AustraliaResearch School of Earth Sciences, Australian National University, Canberra, ACT 2601, AustraliaClimate Change Research Centre, University of New South Wales, Sydney, NSW 2052, AustraliaClimate Change Research Centre, University of New South Wales, Sydney, NSW 2052, AustraliaCSIRO Ecosystem Sciences, Private Bag 5, Wembley, WA 6913, AustraliaARC Centre of Excellence for Climate Extremes, Canberra, ACT 2601, AustraliaResearch School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia<p>Recent experimental evidence suggests that during heat extremes, wooded ecosystems may decouple photosynthesis and transpiration, reducing photosynthesis to near zero but increasing transpiration into the boundary layer. This feedback may act to dampen, rather than amplify, heat extremes in wooded ecosystems. We examined eddy covariance databases (OzFlux and FLUXNET2015) to identify whether there was field-based evidence to support these experimental findings. We focused on two types of heat extremes: (i) the 3 days leading up to a temperature extreme, defined as including a daily maximum temperature <span class="inline-formula">>37</span> <span class="inline-formula"><sup>∘</sup></span>C (similar to the widely used TXx metric), and (ii) heatwaves, defined as 3 or more consecutive days above 35 <span class="inline-formula"><sup>∘</sup></span>C. When focusing on (i), we found some evidence of reduced photosynthesis and sustained or increased latent heat fluxes at seven Australian evergreen wooded flux sites. However, when considering the role of vapour pressure deficit and focusing on (ii), we were unable to conclusively disentangle the decoupling between photosynthesis and latent heat flux from the effect of increasing the vapour pressure deficit. Outside of Australia, the Tier-1 FLUXNET2015 database provided limited scope to tackle this issue as it does not sample sufficient high temperature events with which to probe the physiological response of trees to extreme heat. Thus, further work is required to determine whether this photosynthetic decoupling occurs widely, ideally by matching experimental species with those found at eddy covariance tower sites. Such measurements would allow this decoupling mechanism to be probed experimentally and at the ecosystem scale. Transpiration during heatwaves remains a key issue to resolve, as no land surface model includes a decoupling mechanism, and any potential dampening of the land–atmosphere amplification is thus not included in climate model projections.</p>https://www.biogeosciences.net/16/903/2019/bg-16-903-2019.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
M. G. De Kauwe M. G. De Kauwe B. E. Medlyn A. J. Pitman A. J. Pitman J. E. Drake A. Ukkola A. Ukkola A. Griebel E. Pendall S. Prober M. Roderick M. Roderick |
spellingShingle |
M. G. De Kauwe M. G. De Kauwe B. E. Medlyn A. J. Pitman A. J. Pitman J. E. Drake A. Ukkola A. Ukkola A. Griebel E. Pendall S. Prober M. Roderick M. Roderick Examining the evidence for decoupling between photosynthesis and transpiration during heat extremes Biogeosciences |
author_facet |
M. G. De Kauwe M. G. De Kauwe B. E. Medlyn A. J. Pitman A. J. Pitman J. E. Drake A. Ukkola A. Ukkola A. Griebel E. Pendall S. Prober M. Roderick M. Roderick |
author_sort |
M. G. De Kauwe |
title |
Examining the evidence for decoupling between photosynthesis and transpiration during heat extremes |
title_short |
Examining the evidence for decoupling between photosynthesis and transpiration during heat extremes |
title_full |
Examining the evidence for decoupling between photosynthesis and transpiration during heat extremes |
title_fullStr |
Examining the evidence for decoupling between photosynthesis and transpiration during heat extremes |
title_full_unstemmed |
Examining the evidence for decoupling between photosynthesis and transpiration during heat extremes |
title_sort |
examining the evidence for decoupling between photosynthesis and transpiration during heat extremes |
publisher |
Copernicus Publications |
series |
Biogeosciences |
issn |
1726-4170 1726-4189 |
publishDate |
2019-02-01 |
description |
<p>Recent experimental evidence suggests that during heat extremes, wooded
ecosystems may decouple photosynthesis and transpiration, reducing
photosynthesis to near zero but increasing transpiration into the boundary
layer. This feedback may act to dampen, rather than amplify, heat extremes in
wooded ecosystems. We examined eddy covariance databases (OzFlux and
FLUXNET2015) to identify whether there was field-based evidence to support
these experimental findings. We focused on two types of heat extremes:
(i) the 3 days leading up to a temperature extreme, defined as including
a daily maximum temperature <span class="inline-formula">>37</span> <span class="inline-formula"><sup>∘</sup></span>C (similar to the widely used
TXx metric), and (ii) heatwaves, defined as 3 or more consecutive days
above 35 <span class="inline-formula"><sup>∘</sup></span>C. When focusing on (i), we found some evidence of
reduced photosynthesis and sustained or increased latent heat fluxes at seven
Australian evergreen wooded flux sites. However, when considering the role of
vapour pressure deficit and focusing on (ii), we were unable to conclusively
disentangle the decoupling between photosynthesis and latent heat flux from
the effect of increasing the vapour pressure deficit. Outside of Australia, the
Tier-1 FLUXNET2015 database provided limited scope to tackle this issue as it
does not sample sufficient high temperature events with which to probe the
physiological response of trees to extreme heat. Thus, further work is
required to determine whether this photosynthetic decoupling occurs widely,
ideally by matching experimental species with those found at eddy covariance
tower sites. Such measurements would allow this decoupling mechanism to be
probed experimentally and at the ecosystem scale. Transpiration during
heatwaves remains a key issue to resolve, as no land surface model includes a
decoupling mechanism, and any potential dampening of the land–atmosphere
amplification is thus not included in climate model projections.</p> |
url |
https://www.biogeosciences.net/16/903/2019/bg-16-903-2019.pdf |
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