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

Sönke Zaehle*, Belinda E. Medlyn, Martin G. De Kauwe, Anthony P. Walker, Michael C. Dietze, Thomas Hickler, Yiqi Luo, Ying Ping Wang, Bassil El-Masri, Peter Thornton, Atul Jain, Shusen Wang, David Warlind, Ensheng Weng, William Parton, Colleen M. Iversen, Anne Gallet-Budynek, Heather Mccarthy, Adrien Finzi, Paul J. HansonI. Colin Prentice, Ram Oren, Richard J. Norby

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

240 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)803-822
Number of pages20
JournalNew Phytologist
Volume202
Issue number3
DOIs
Publication statusPublished - May 2014

Keywords

  • Carbon (C) storage
  • Ecosystem modelling
  • Model evaluation
  • Nitrogen (N) limitation
  • Plant physiology

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