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Title: 20th century changes in carbon isotopes and water-use efficiency: tree-ring-based evaluation of the CLM4.5 and LPX-Bern models

Abstract

Measurements of the stable carbon isotope ratio ( δ 13C) on annual tree rings offer new opportunities to evaluate mechanisms of variations in photosynthesis and stomatal conductance under changing CO 2 and climate conditions, especially in conjunction with process-based biogeochemical model simulations. The isotopic discrimination is indicative of the ratio between the CO 2 partial pressure in the intercellular cavities and the atmosphere ( c i/ c a) and of the ratio of assimilation to stomatal conductance, termed intrinsic water-use efficiency (iWUE). We performed isotope-enabled simulations over the industrial period with the land biosphere module (CLM4.5) of the Community Earth System Model and the Land Surface Processes and Exchanges (LPX-Bern) dynamic global vegetation model. Results for C3 tree species show good agreement with a global compilation of δ 13C measurements on leaves, though modeled 13C discrimination by C3 trees is smaller in arid regions than measured. A compilation of 76 tree-ring records, mainly from Europe, boreal Asia, and western North America, suggests on average small 20th century changes in isotopic discrimination and in c i/ c a and an increase in iWUE of about 27% since 1900. LPX-Bern results match these century-scale reconstructions, supporting the idea that the physiology of stomatamore » has evolved to optimize trade-offs between carbon gain by assimilation and water loss by transpiration. In contrast, CLM4.5 simulates an increase in discrimination and in turn a change in iWUE that is almost twice as large as that revealed by the tree-ring data. Factorial simulations show that these changes are mainly in response to rising atmospheric CO 2. The results suggest that the downregulation of c i/ c a and of photosynthesis by nitrogen limitation is possibly too strong in the standard setup of CLM4.5 or that there may be problems associated with the implementation of conductance, assimilation, and related adjustment processes on long-term environmental changes.« less

Authors:
 [1];  [1];  [1];  [1]; ORCiD logo [2];  [3];  [3]; ORCiD logo [4]; ORCiD logo [1];  [4];  [5];  [5];  [6];  [1]
  1. Univ. of Bern (Switzerland)
  2. (Sidorova), Olga V. [Siberian Federal Univ., Krasnoyarsk (Russia); Univ. of Geneva (Switzerland)
  3. Univ. of Bern (Switzerland); Univ. of Arizona, Tucson, AZ (United States); Swiss Federal Research Inst., Birmensdorf (Switzerland)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  5. Paul Scherrer Inst. (PSI), Villigen (Switzerland); Swiss Federal Research Inst., Birmensdorf (Switzerland)
  6. Paul Scherrer Inst. (PSI), Villigen (Switzerland)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1379862
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Biogeosciences (Online)
Additional Journal Information:
Journal Name: Biogeosciences (Online); Journal Volume: 14; Journal Issue: 10; Journal ID: ISSN 1726-4189
Publisher:
European Geosciences Union
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES

Citation Formats

Keller, Kathrin M., Lienert, Sebastian, Bozbiyik, Anil, Stocker, Thomas F., Churakova, Frank, David C., Klesse, Stefan, Koven, Charles D., Leuenberger, Markus, Riley, William J., Saurer, Matthias, Siegwolf, Rolf, Weigt, Rosemarie B., and Joos, Fortunat. 20th century changes in carbon isotopes and water-use efficiency: tree-ring-based evaluation of the CLM4.5 and LPX-Bern models. United States: N. p., 2017. Web. doi:10.5194/bg-14-2641-2017.
Keller, Kathrin M., Lienert, Sebastian, Bozbiyik, Anil, Stocker, Thomas F., Churakova, Frank, David C., Klesse, Stefan, Koven, Charles D., Leuenberger, Markus, Riley, William J., Saurer, Matthias, Siegwolf, Rolf, Weigt, Rosemarie B., & Joos, Fortunat. 20th century changes in carbon isotopes and water-use efficiency: tree-ring-based evaluation of the CLM4.5 and LPX-Bern models. United States. doi:10.5194/bg-14-2641-2017.
Keller, Kathrin M., Lienert, Sebastian, Bozbiyik, Anil, Stocker, Thomas F., Churakova, Frank, David C., Klesse, Stefan, Koven, Charles D., Leuenberger, Markus, Riley, William J., Saurer, Matthias, Siegwolf, Rolf, Weigt, Rosemarie B., and Joos, Fortunat. Wed . "20th century changes in carbon isotopes and water-use efficiency: tree-ring-based evaluation of the CLM4.5 and LPX-Bern models". United States. doi:10.5194/bg-14-2641-2017. https://www.osti.gov/servlets/purl/1379862.
@article{osti_1379862,
title = {20th century changes in carbon isotopes and water-use efficiency: tree-ring-based evaluation of the CLM4.5 and LPX-Bern models},
author = {Keller, Kathrin M. and Lienert, Sebastian and Bozbiyik, Anil and Stocker, Thomas F. and Churakova and Frank, David C. and Klesse, Stefan and Koven, Charles D. and Leuenberger, Markus and Riley, William J. and Saurer, Matthias and Siegwolf, Rolf and Weigt, Rosemarie B. and Joos, Fortunat},
abstractNote = {Measurements of the stable carbon isotope ratio (δ13C) on annual tree rings offer new opportunities to evaluate mechanisms of variations in photosynthesis and stomatal conductance under changing CO2 and climate conditions, especially in conjunction with process-based biogeochemical model simulations. The isotopic discrimination is indicative of the ratio between the CO2 partial pressure in the intercellular cavities and the atmosphere (ci/ca) and of the ratio of assimilation to stomatal conductance, termed intrinsic water-use efficiency (iWUE). We performed isotope-enabled simulations over the industrial period with the land biosphere module (CLM4.5) of the Community Earth System Model and the Land Surface Processes and Exchanges (LPX-Bern) dynamic global vegetation model. Results for C3 tree species show good agreement with a global compilation of δ13C measurements on leaves, though modeled 13C discrimination by C3 trees is smaller in arid regions than measured. A compilation of 76 tree-ring records, mainly from Europe, boreal Asia, and western North America, suggests on average small 20th century changes in isotopic discrimination and in ci/ca and an increase in iWUE of about 27% since 1900. LPX-Bern results match these century-scale reconstructions, supporting the idea that the physiology of stomata has evolved to optimize trade-offs between carbon gain by assimilation and water loss by transpiration. In contrast, CLM4.5 simulates an increase in discrimination and in turn a change in iWUE that is almost twice as large as that revealed by the tree-ring data. Factorial simulations show that these changes are mainly in response to rising atmospheric CO2. The results suggest that the downregulation of ci/ca and of photosynthesis by nitrogen limitation is possibly too strong in the standard setup of CLM4.5 or that there may be problems associated with the implementation of conductance, assimilation, and related adjustment processes on long-term environmental changes.},
doi = {10.5194/bg-14-2641-2017},
journal = {Biogeosciences (Online)},
number = 10,
volume = 14,
place = {United States},
year = {Wed May 24 00:00:00 EDT 2017},
month = {Wed May 24 00:00:00 EDT 2017}
}

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