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Forest water use and water use efficiency at elevated CO2: a model-data intercomparison at two contrasting temperate forest FACE sites

De Kauwe, Martin G.; Medlyn, Belinda E.; Zaehle, Soenke; Walker, Anthony P.; Dietze, Michael C.; Hickler, Thomas; Jain, Atul K.; Luo, Yiqi; Parton, William J. and Prentice, I. Colin, et al. (2013) In Global Change Biology 19(6). p.1759-1779
Abstract
Predicted responses of transpiration to elevated atmospheric CO2 concentration (eCO2) are highly variable amongst process-based models. To better understand and constrain this variability amongst models, we conducted an intercomparison of 11 ecosystem models applied to data from two forest free-air CO2 enrichment (FACE) experiments at Duke University and Oak Ridge National Laboratory. We analysed model structures to identify the key underlying assumptions causing differences in model predictions of transpiration and canopy water use efficiency. We then compared the models against data to identify model assumptions that are incorrect or are large sources of uncertainty. We found that model-to-model and model-to-observations differences... (More)
Predicted responses of transpiration to elevated atmospheric CO2 concentration (eCO2) are highly variable amongst process-based models. To better understand and constrain this variability amongst models, we conducted an intercomparison of 11 ecosystem models applied to data from two forest free-air CO2 enrichment (FACE) experiments at Duke University and Oak Ridge National Laboratory. We analysed model structures to identify the key underlying assumptions causing differences in model predictions of transpiration and canopy water use efficiency. We then compared the models against data to identify model assumptions that are incorrect or are large sources of uncertainty. We found that model-to-model and model-to-observations differences resulted from four key sets of assumptions, namely (i) the nature of the stomatal response to elevated CO2 (coupling between photosynthesis and stomata was supported by the data); (ii) the roles of the leaf and atmospheric boundary layer (models which assumed multiple conductance terms in series predicted more decoupled fluxes than observed at the broadleaf site); (iii) the treatment of canopy interception (large intermodel variability, 215%); and (iv) the impact of soil moisture stress (process uncertainty in how models limit carbon and water fluxes during moisture stress). Overall, model predictions of the CO2 effect on WUE were reasonable (intermodel =approximately 28%+/- 10%) compared to the observations (=approximately 30%+/- 13%) at the well-coupled coniferous site (Duke), but poor (intermodel =approximately 24%+/- 6%; observations =approximately 38%+/- 7%) at the broadleaf site (Oak Ridge). The study yields a framework for analysing and interpreting model predictions of transpiration responses to eCO2, and highlights key improvements to these types of models. (Less)
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Contribution to journal
publication status
published
subject
keywords
climate change, CO2 fertilization, elevated CO2, FACE, models, plant, physiology, stomatal conductance, water
in
Global Change Biology
volume
19
issue
6
pages
1759 - 1779
publisher
Wiley-Blackwell
external identifiers
  • wos:000318353300010
  • scopus:84877082704
ISSN
1354-1013
DOI
10.1111/gcb.12164
project
MERGE
BECC
language
English
LU publication?
yes
id
de4696f6-af46-4527-b574-36826debe9f8 (old id 3815260)
date added to LUP
2013-06-26 09:10:53
date last changed
2019-02-03 03:33:00
@article{de4696f6-af46-4527-b574-36826debe9f8,
  abstract     = {Predicted responses of transpiration to elevated atmospheric CO2 concentration (eCO2) are highly variable amongst process-based models. To better understand and constrain this variability amongst models, we conducted an intercomparison of 11 ecosystem models applied to data from two forest free-air CO2 enrichment (FACE) experiments at Duke University and Oak Ridge National Laboratory. We analysed model structures to identify the key underlying assumptions causing differences in model predictions of transpiration and canopy water use efficiency. We then compared the models against data to identify model assumptions that are incorrect or are large sources of uncertainty. We found that model-to-model and model-to-observations differences resulted from four key sets of assumptions, namely (i) the nature of the stomatal response to elevated CO2 (coupling between photosynthesis and stomata was supported by the data); (ii) the roles of the leaf and atmospheric boundary layer (models which assumed multiple conductance terms in series predicted more decoupled fluxes than observed at the broadleaf site); (iii) the treatment of canopy interception (large intermodel variability, 215%); and (iv) the impact of soil moisture stress (process uncertainty in how models limit carbon and water fluxes during moisture stress). Overall, model predictions of the CO2 effect on WUE were reasonable (intermodel =approximately 28%+/- 10%) compared to the observations (=approximately 30%+/- 13%) at the well-coupled coniferous site (Duke), but poor (intermodel =approximately 24%+/- 6%; observations =approximately 38%+/- 7%) at the broadleaf site (Oak Ridge). The study yields a framework for analysing and interpreting model predictions of transpiration responses to eCO2, and highlights key improvements to these types of models.},
  author       = {De Kauwe, Martin G. and Medlyn, Belinda E. and Zaehle, Soenke and Walker, Anthony P. and Dietze, Michael C. and Hickler, Thomas and Jain, Atul K. and Luo, Yiqi and Parton, William J. and Prentice, I. Colin and Smith, Benjamin and Thornton, Peter E. and Wang, Shusen and Wang, Ying-Ping and Wårlind, David and Weng, Ensheng and Crous, Kristine Y. and Ellsworth, David S. and Hanson, Paul J. and Seok Kim, Hyun- and Warren, Jeffrey M. and Oren, Ram and Norby, Richard J.},
  issn         = {1354-1013},
  keyword      = {climate change,CO2 fertilization,elevated CO2,FACE,models,plant,physiology,stomatal conductance,water},
  language     = {eng},
  number       = {6},
  pages        = {1759--1779},
  publisher    = {Wiley-Blackwell},
  series       = {Global Change Biology},
  title        = {Forest water use and water use efficiency at elevated CO2: a model-data intercomparison at two contrasting temperate forest FACE sites},
  url          = {http://dx.doi.org/10.1111/gcb.12164},
  volume       = {19},
  year         = {2013},
}