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

• Published in: The New phytologist Vol. 202; no. 3; pp. 803 - 822
• Main Authors: Zaehle, Sönke, Medlyn, Belinda E, De Kauwe, Martin G, Walker, Anthony P, Dietze, Michael C, Hickler, Thomas, Luo, Yiqi, Wang, Ying‐Ping, El‐Masri, Bassil, Thornton, Peter, Jain, Atul, Wang, Shusen, Warlind, David, Weng, Ensheng, Parton, William, Iversen, Colleen M, Gallet‐Budynek, Anne, McCarthy, Heather, Finzi, Adrien, Hanson, Paul J, Prentice, I. Colin, Oren, Ram, Norby, Richard J
• Format: Journal Article
• Language: English
• Published: England William Wesley and Son 01.05.2014; New Phytologist Trust; Wiley Subscription Services, Inc; Wiley; BlackWell Publishing Ltd
• Subjects: Air; Atmosphere - chemistry; Atmospheric models; Biomass; carbon; carbon (C) storage; Carbon - metabolism; Carbon Cycle; Carbon dioxide; Carbon Dioxide - metabolism; CO2; CO2 fertilization; Earth and Related Environmental Sciences; Ecosystem; ecosystem modelling; Ecosystem models; elevated; elevated CO2; Enrichment; Enrichment (FACE); Environment models; Environmental Sciences; Experiments; Forest ecosystems; Forest Science; Forest soils; free air carbon dioxide enrichment; Free-Air CO2; Free‐Air CO2 Enrichment (FACE); Geovetenskap och miljövetenskap; Global Changes; inventories; Life Sciences; limitation; model evaluation; Modeling; Models, Biological; Natural Sciences; Naturgeografi; Naturvetenskap; Net Primary Productivity; Nitrogen; nitrogen (N); nitrogen (N) limitation; Nitrogen - metabolism; Nitrogen Cycle; Organic matter; Organic soils; Physical Geography; plant physiology; Plants; Primary production; primary productivity; Qualitative analysis; Representations; Research facilities; Skogsvetenskap; Soil ecology; Soil organic matter; Stoichiometry; Temperate forests; Terrestrial ecosystems; Terrestrial environments; Time Factors; Trends; uncertainty; Uptake; Vegetal Biology; Vegetation; plant physiology; carbon (C) storage; ecosystem modelling; model evaluation; elevated CO2; CO2 fertilization; Free-Air CO2 Enrichment (FACE); nitrogen (N) limitation; Free-Air CO2Enrichment (FACE)
• ISSN: 0028-646X; 1469-8137; 1469-8137
• DOI: 10.1111/nph.12697

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.