Evaluation of 11 terrestrial carbon-nitrogen cycle models against observations from two temperate Free-Air CO2 Enrichment studies.
We analysed the responses of 11 ecosystem models to elevated atmospheric [CO2 ] (eCO2 ) at two temperate forest ecosystems (Duke and Oak Ridge National Laboratory (ORNL) Free-Air CO2 Enrichment (FACE) experiments) to test alternative representations of carbon (C)-nitrogen (N) cycle processes. We decomposed the model responses into component processes affecting the response to eCO2 and confronted these with observations from the FACE experiments. Most of the models reproduced the observed initial enhancement of net primary production (NPP) at both sites, but none was able to simulate both the sustained 10-yr enhancement at Duke and the declining response at ORNL: models generally showed signs of progressive N limitation as a result of lower than observed plant N uptake. Nonetheless, many models showed qualitative agreement with observed component processes. The results suggest that improved representation of above-ground-below-ground interactions and better constraints on plant stoichiometry are important for a predictive understanding of eCO2 effects. Improved accuracy of soil organic matter inventories is pivotal to reduce uncertainty in the observed C-N budgets. The two FACE experiments are insufficient to fully constrain terrestrial responses to eCO2 , given the complexity of factors leading to the observed diverging trends, and the consequential inability of the models to explain these trends. Nevertheless, the ecosystem models were able to capture important features of the experiments, lending some support to their projections.
Biogeochemical Integration Department, Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, D-07745, Jena, Germany.
Sönke
S
Zaehle
Department of Biological Science, Macquarie University, Sydney, NSW, 2109, Australia.
Belinda E
BE
Medlyn
Department of Biological Science, Macquarie University, Sydney, NSW, 2109, Australia.
Martin G
MG
De Kauwe
Oak Ridge National Laboratory, Environmental Sciences Division, Climate Change Science Institute, Oak Ridge, TN, 37831, USA.
Anthony P
AP
Walker
Department of Earth and Environment, Boston University, Boston, MA, 02215, USA.
Michael C
MC
Dietze
Biodiversity and Climate Research Centre (BiK-F), Senckenberg Gesellschaft für Naturforschung, D-60325, Frankfurt am Main, Germany.|Department of Physical Geography, Goethe University, D-60438, Frankfurt am Main, Germany.
Thomas
T
Hickler
Department of Microbiology & Plant Biology, University of Oklahoma, Norman, OK, 73019, USA.
Yiqi
Y
Luo
CSIRO Marine and Atmospheric Research, PMB 1, Aspendale, Vic., 3195, Australia.
Ying-Ping
YP
Wang
Department of Atmospheric Sciences, University of Illinois, Urbana, IL, 61801, USA.
Bassil
B
El-Masri
Oak Ridge National Laboratory, Environmental Sciences Division, Climate Change Science Institute, Oak Ridge, TN, 37831, USA.
Peter
P
Thornton
Department of Atmospheric Sciences, University of Illinois, Urbana, IL, 61801, USA.
Atul
A
Jain
Canada Centre for Mapping and Earth Observation, Natural Resources Canada, Ottawa, ON, K1A 0Y7, Canada.
Shusen
S
Wang
Department of Physical Geography and Ecosystem Science, Lund University, SE-22362, Lund, Sweden.
David
D
Warlind
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, 08544, USA.
Ensheng
E
Weng
Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523, USA.
William
W
Parton
Oak Ridge National Laboratory, Environmental Sciences Division, Climate Change Science Institute, Oak Ridge, TN, 37831, USA.
Colleen M
CM
Iversen
INRA, UMR1220 TCEM, F-33882, Villenave d'Ornon, France.|Université de Bordeaux, UMR1220 TCEM, F-33175, Gradignan, France.
Anne
A
Gallet-Budynek
Department of Microbiology & Plant Biology, University of Oklahoma, Norman, OK, 73019, USA.
Heather
H
McCarthy
Department of Biology, Boston University, Boston, MA, 02215, USA.
Adrien
A
Finzi
Oak Ridge National Laboratory, Environmental Sciences Division, Climate Change Science Institute, Oak Ridge, TN, 37831, USA.
Paul J
PJ
Hanson
Department of Biological Science, Macquarie University, Sydney, NSW, 2109, Australia.|AXA Chair of Biosphere and Climate Impacts, Department of Life Sciences and Grantham Institute for Climate Change, Imperial College London, Silwood Park, Ascot, SL5 7PY, UK.
I Colin
IC
Prentice
Division of Environmental Science & Policy, Nicholas School of the Environment, Duke University, Durham, NC, 27708, USA.|Department of Forest Ecology & Management, Swedish University of Agricultural Sciences (SLU), SE-901 83, Umeå, Sweden.
Ram
R
Oren
Oak Ridge National Laboratory, Environmental Sciences Division, Climate Change Science Institute, Oak Ridge, TN, 37831, USA.
Richard J
RJ
Norby
D000388:Air; D001272:Atmosphere / Q000737:chemistry; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D017753:Ecosystem; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism; D058458:Nitrogen Cycle; D013997:Time Factors
D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen
CO2 fertilization; Free-Air CO2 Enrichment (FACE); carbon (C) storage; ecosystem modelling; elevated CO2; model evaluation; nitrogen (N) limitation; plant physiology