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Title: The quasi-equilibrium framework revisited: analyzing long-term CO 2 enrichment responses in plant–soil models

Abstract

Abstract. Elevated carbon dioxide (CO 2) can increase plant growth, but themagnitude of this CO 2 fertilization effect is modified by soilnutrient availability. Predicting how nutrient availability affects plantresponses to elevated CO 2 is a key consideration for ecosystemmodels, and many modeling groups have moved to, or are moving towards,incorporating nutrient limitation in their models. The choice of assumptionsto represent nutrient cycling processes has a major impact on modelpredictions, but it can be difficult to attribute outcomes to specificassumptions in complex ecosystem simulation models. Here we revisit thequasi-equilibrium analytical framework introduced by Comins andMcMurtrie (1993) and explore the consequences of specific model assumptionsfor ecosystem net primary productivity (NPP). We review the literature applying this framework to plant–soilmodels and then analyze the effect of several new assumptions on predictedplant responses to elevated CO 2. Examination of alternativeassumptions for plant nitrogen uptake showed that a linear function of themineral nitrogen pool or a linear function of the mineral nitrogen pool withan additional saturating function of root biomass yield similar CO 2responses at longer timescales (>5 years), suggesting that the addedcomplexity may not be needed when these are the timescales of interest. Incontrast, a saturating function of the mineral nitrogen pool with lineardependency on rootmore » biomass yields no soil nutrient feedback on thevery-long-term (>500 years), near-equilibrium timescale, meaning that oneshould expect the model to predict a full CO 2 fertilization effecton production. Secondly, we show that incorporating a priming effect on slowsoil organic matter decomposition attenuates the nutrient feedback effect onproduction, leading to a strong medium-term (5–50 years) CO 2response. Models incorporating this priming effect should thus predict astrong and persistent CO 2 fertilization effect over time. Thirdly,we demonstrate that using a “potential NPP” approach to represent nutrientlimitation of growth yields a relatively small CO 2 fertilizationeffect across all timescales. Overall, our results highlight thefact that the quasi-equilibriumanalytical framework is effective for evaluating both the consequences andmechanisms through which different model assumptions affect predictions. Tohelp constrain predictions of the future terrestrial carbon sink, werecommend the use of this framework to analyze likely outcomes of new modelassumptions before introducing them to complex model structures.« less

Authors:
 [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [2];  [1];  [1]
  1. Western Sydney Univ., Penrith, NSW (Australia)
  2. Max Planck Institute of Biogeochemistry, Jena (Germany)
  3. Univ. of New South Wales, Sydney, NSW (Australia)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1558493
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Geoscientific Model Development (Online)
Additional Journal Information:
Journal Name: Geoscientific Model Development (Online); Journal Volume: 12; Journal Issue: 5; Journal ID: ISSN 1991-9603
Publisher:
European Geosciences Union
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Jiang, Mingkai, Zaehle, Sönke, De Kauwe, Martin G., Walker, Anthony P., Caldararu, Silvia, Ellsworth, David S., and Medlyn, Belinda E. The quasi-equilibrium framework revisited: analyzing long-term CO2 enrichment responses in plant–soil models. United States: N. p., 2019. Web. doi:10.5194/gmd-12-2069-2019.
Jiang, Mingkai, Zaehle, Sönke, De Kauwe, Martin G., Walker, Anthony P., Caldararu, Silvia, Ellsworth, David S., & Medlyn, Belinda E. The quasi-equilibrium framework revisited: analyzing long-term CO2 enrichment responses in plant–soil models. United States. doi:10.5194/gmd-12-2069-2019.
Jiang, Mingkai, Zaehle, Sönke, De Kauwe, Martin G., Walker, Anthony P., Caldararu, Silvia, Ellsworth, David S., and Medlyn, Belinda E. Tue . "The quasi-equilibrium framework revisited: analyzing long-term CO2 enrichment responses in plant–soil models". United States. doi:10.5194/gmd-12-2069-2019. https://www.osti.gov/servlets/purl/1558493.
@article{osti_1558493,
title = {The quasi-equilibrium framework revisited: analyzing long-term CO2 enrichment responses in plant–soil models},
author = {Jiang, Mingkai and Zaehle, Sönke and De Kauwe, Martin G. and Walker, Anthony P. and Caldararu, Silvia and Ellsworth, David S. and Medlyn, Belinda E.},
abstractNote = {Abstract. Elevated carbon dioxide (CO2) can increase plant growth, but themagnitude of this CO2 fertilization effect is modified by soilnutrient availability. Predicting how nutrient availability affects plantresponses to elevated CO2 is a key consideration for ecosystemmodels, and many modeling groups have moved to, or are moving towards,incorporating nutrient limitation in their models. The choice of assumptionsto represent nutrient cycling processes has a major impact on modelpredictions, but it can be difficult to attribute outcomes to specificassumptions in complex ecosystem simulation models. Here we revisit thequasi-equilibrium analytical framework introduced by Comins andMcMurtrie (1993) and explore the consequences of specific model assumptionsfor ecosystem net primary productivity (NPP). We review the literature applying this framework to plant–soilmodels and then analyze the effect of several new assumptions on predictedplant responses to elevated CO2. Examination of alternativeassumptions for plant nitrogen uptake showed that a linear function of themineral nitrogen pool or a linear function of the mineral nitrogen pool withan additional saturating function of root biomass yield similar CO2responses at longer timescales (>5 years), suggesting that the addedcomplexity may not be needed when these are the timescales of interest. Incontrast, a saturating function of the mineral nitrogen pool with lineardependency on root biomass yields no soil nutrient feedback on thevery-long-term (>500 years), near-equilibrium timescale, meaning that oneshould expect the model to predict a full CO2 fertilization effecton production. Secondly, we show that incorporating a priming effect on slowsoil organic matter decomposition attenuates the nutrient feedback effect onproduction, leading to a strong medium-term (5–50 years) CO2response. Models incorporating this priming effect should thus predict astrong and persistent CO2 fertilization effect over time. Thirdly,we demonstrate that using a “potential NPP” approach to represent nutrientlimitation of growth yields a relatively small CO2 fertilizationeffect across all timescales. Overall, our results highlight thefact that the quasi-equilibriumanalytical framework is effective for evaluating both the consequences andmechanisms through which different model assumptions affect predictions. Tohelp constrain predictions of the future terrestrial carbon sink, werecommend the use of this framework to analyze likely outcomes of new modelassumptions before introducing them to complex model structures.},
doi = {10.5194/gmd-12-2069-2019},
journal = {Geoscientific Model Development (Online)},
number = 5,
volume = 12,
place = {United States},
year = {2019},
month = {5}
}

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