Predicting long‐term carbon sequestration in response to CO2 enrichment: How and why do current ecosystem models differ?. Issue 4 (27th April 2015)

• Record Type: Journal Article
• Authors: Walker, Anthony P.; Zaehle, Sönke; Medlyn, Belinda E.; De Kauwe, Martin G.; Asao, Shinichi; Hickler, Thomas; Parton, William; Ricciuto, Daniel M.; Wang, Ying‐Ping; Wårlind, David; Norby, Richard J.
• Is Part Of: Global biogeochemical cycles. Volume 29:Issue 4(2015:Apr.)
• Page Start: 476
• Page End: 495
• Publication Date: 2015-04-27
• Subjects: Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2014GB004995
• Languages: English
• ISSNs: 0886-6236

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>Large uncertainty exists in model projections of the land carbon (C) sink response to increasing atmospheric CO<sub>2</sub>. Free‐Air CO<sub>2</sub> Enrichment (FACE) experiments lasting a decade or more have investigated ecosystem responses to a step change in atmospheric CO<sub>2</sub> concentration. To interpret FACE results in the context of gradual increases in atmospheric CO<sub>2</sub> over decades to centuries, we used a suite of seven models to simulate the Duke and Oak Ridge FACE experiments extended for 300 years of CO<sub>2</sub> enrichment. We also determine key modeling assumptions that drive divergent projections of terrestrial C uptake and evaluate whether these assumptions can be constrained by experimental evidence. All models simulated increased terrestrial C pools resulting from CO<sub>2</sub> enrichment, though there was substantial variability in quasi‐equilibrium C sequestration and rates of change. In two of two models that assume that plant nitrogen (N) uptake is solely a function of soil N supply, the net primary production response to elevated CO<sub>2</sub> became progressively N limited. In four of five models that assume that N uptake is a function of both soil N supply and plant N demand, elevated CO<sub>2</sub> led to reduced ecosystem N losses and thus progressively relaxed nitrogen limitation. Many allocation assumptions resulted in increased wood allocation relative to leaves and roots which reduced the vegetation turnover rate and increased C sequestration. In addition, self‐thinning assumptions had a substantial impact on C sequestration in two models. Accurate representation of N process dynamics (in particular N uptake), allocation, and forest self‐thinning is key to minimizing uncertainty in projections of future C sequestration in response to elevated atmospheric CO<sub>2</sub>.</p> </abstract>