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Evaluation of 11 terrestrial carbon-nitrogen cycle models against observations from two temperate Free-Air CO2 Enrichment studies

Zaehle, Soenke ; Medlyn, Belinda E. ; De Kauwe, Martin G. ; Walker, Anthony P. ; Dietze, Michael C. ; Hickler, Thomas ; Luo, Yiqi ; Wang, Ying-Ping ; El-Masri, Bassil and Thornton, Peter , et al. (2014) In New Phytologist 202(3). p.803-822
Abstract
We analysed the responses of 11 ecosystem models to elevated atmospheric [CO2] (eCO(2)) 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 eCO(2) 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... (More)
We analysed the responses of 11 ecosystem models to elevated atmospheric [CO2] (eCO(2)) 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 eCO(2) 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 eCO(2) 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 eCO(2), 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. (Less)
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@article{a0e09ffb-98b8-4e65-8998-d0db6566d2d2,
  abstract     = {We analysed the responses of 11 ecosystem models to elevated atmospheric [CO2] (eCO(2)) 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 eCO(2) 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 eCO(2) 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 eCO(2), 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.},
  author       = {Zaehle, Soenke and Medlyn, Belinda E. and De Kauwe, Martin G. and Walker, Anthony P. and Dietze, Michael C. and Hickler, Thomas and Luo, Yiqi and Wang, Ying-Ping and El-Masri, Bassil and Thornton, Peter and Jain, Atul and Wang, Shusen and Wårlind, David and Weng, Ensheng and Parton, William and Iversen, Colleen M. and Gallet-Budynek, Anne and McCarthy, Heather and Finzi, Adrien and Hanson, Paul J. and Prentice, I. Colin and Oren, Ram and Norby, Richard J.},
  issn         = {1469-8137},
  language     = {eng},
  number       = {3},
  pages        = {803--822},
  publisher    = {Wiley-Blackwell},
  series       = {New Phytologist},
  title        = {Evaluation of 11 terrestrial carbon-nitrogen cycle models against observations from two temperate Free-Air CO2 Enrichment studies},
  url          = {http://dx.doi.org/10.1111/nph.12697},
  doi          = {10.1111/nph.12697},
  volume       = {202},
  year         = {2014},
}