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

Zaehle S, Medlyn BE, De Kauwe MG, Walker AP, Dietze MC, Hickler T, Luo Y, Wang YP, El-Masri B, Thornton P, Jain A, Wang S, Warlind D, Weng E, Parton W, Iversen CM, Gallet-Budynek A, McCarthy H, Finzi A, Hanson PJ, Prentice IC, Oren R, Norby RJ - New Phytol. (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Biogeochemical Integration Department, Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, D-07745, Jena, Germany.

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Conceptual diagram of the major nitrogen (N) and carbon (C) flows and stores in a terrestrial ecosystem. Blue arrows denote C fluxes and red arrows N fluxes between major plant compartments (green) and soil pools (black). Numbers 1–5 mark important C–N cycle linkages as described in the Evaluation framework section: 1, N-based gross primary production (GPPN): the return of C assimilates per unit canopy N Eqn 1; 2, whole-plant nitrogen-use efficiency (NUE): the total amount of foliar, root and woody production per unit of N taken up by plants; this process depends on the allocation of growth between different plant compartments (e.g. leaves, fine roots and wood) and the C : N stoichiometry of each compartment Eqn 2; 3, plant N uptake (fNup): the capacity of the plants to take up N from the soil Eqn 4. The plant-available soil N is determined by two factors: 4, net N mineralization (fNmin): the amount of N liberated from organic material through decomposition, which varies with microbial activity and litter quality Eqn 6; and 5, the net ecosystem nitrogen exchange (NNE): based on N inputs from biological N fixation (fNfix) and atmospheric deposition (fNdep) and N losses from the ecosystem as a result of leaching to groundwater (fNleach) and gaseous emission (fNgas) Eqn 5. As an emergent property, the net amount of C that can be stored in an ecosystem following an increase in CO2 depends on the elevated atmospheric [CO2] (eCO2) effect on the ecosystem's N balance and the whole-ecosystem stoichiometry, which, in turn, depends on the change in the C : N stoichiometry of vegetation and soil, as well as the partitioning of N between vegetation and soil (Rastetter et al., 1992).
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fig01: Conceptual diagram of the major nitrogen (N) and carbon (C) flows and stores in a terrestrial ecosystem. Blue arrows denote C fluxes and red arrows N fluxes between major plant compartments (green) and soil pools (black). Numbers 1–5 mark important C–N cycle linkages as described in the Evaluation framework section: 1, N-based gross primary production (GPPN): the return of C assimilates per unit canopy N Eqn 1; 2, whole-plant nitrogen-use efficiency (NUE): the total amount of foliar, root and woody production per unit of N taken up by plants; this process depends on the allocation of growth between different plant compartments (e.g. leaves, fine roots and wood) and the C : N stoichiometry of each compartment Eqn 2; 3, plant N uptake (fNup): the capacity of the plants to take up N from the soil Eqn 4. The plant-available soil N is determined by two factors: 4, net N mineralization (fNmin): the amount of N liberated from organic material through decomposition, which varies with microbial activity and litter quality Eqn 6; and 5, the net ecosystem nitrogen exchange (NNE): based on N inputs from biological N fixation (fNfix) and atmospheric deposition (fNdep) and N losses from the ecosystem as a result of leaching to groundwater (fNleach) and gaseous emission (fNgas) Eqn 5. As an emergent property, the net amount of C that can be stored in an ecosystem following an increase in CO2 depends on the elevated atmospheric [CO2] (eCO2) effect on the ecosystem's N balance and the whole-ecosystem stoichiometry, which, in turn, depends on the change in the C : N stoichiometry of vegetation and soil, as well as the partitioning of N between vegetation and soil (Rastetter et al., 1992).

Mentions: Our study forms part of a model intercomparison (A. P. Walker et al., unpublished) looking at the effect of eCO2 on water (De Kauwe et al., 2013), C (M. G. De Kauwe et al., unpublished) and N cycling. Each of the participating models incorporates the major processes by which the N cycle affects the ecosystem's response to eCO2, such as plant N uptake, net N mineralization and the ecosystem N balance, as well as emergent ecosystem properties, such as the N-use efficiency (NUE) of plant production (Fig.1). The representation of these processes varies greatly among models (Table1), illustrating a lack of consensus on the nature of the mechanisms driving these processes. Our objectives in this study were as follows:


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

Zaehle S, Medlyn BE, De Kauwe MG, Walker AP, Dietze MC, Hickler T, Luo Y, Wang YP, El-Masri B, Thornton P, Jain A, Wang S, Warlind D, Weng E, Parton W, Iversen CM, Gallet-Budynek A, McCarthy H, Finzi A, Hanson PJ, Prentice IC, Oren R, Norby RJ - New Phytol. (2014)

Conceptual diagram of the major nitrogen (N) and carbon (C) flows and stores in a terrestrial ecosystem. Blue arrows denote C fluxes and red arrows N fluxes between major plant compartments (green) and soil pools (black). Numbers 1–5 mark important C–N cycle linkages as described in the Evaluation framework section: 1, N-based gross primary production (GPPN): the return of C assimilates per unit canopy N Eqn 1; 2, whole-plant nitrogen-use efficiency (NUE): the total amount of foliar, root and woody production per unit of N taken up by plants; this process depends on the allocation of growth between different plant compartments (e.g. leaves, fine roots and wood) and the C : N stoichiometry of each compartment Eqn 2; 3, plant N uptake (fNup): the capacity of the plants to take up N from the soil Eqn 4. The plant-available soil N is determined by two factors: 4, net N mineralization (fNmin): the amount of N liberated from organic material through decomposition, which varies with microbial activity and litter quality Eqn 6; and 5, the net ecosystem nitrogen exchange (NNE): based on N inputs from biological N fixation (fNfix) and atmospheric deposition (fNdep) and N losses from the ecosystem as a result of leaching to groundwater (fNleach) and gaseous emission (fNgas) Eqn 5. As an emergent property, the net amount of C that can be stored in an ecosystem following an increase in CO2 depends on the elevated atmospheric [CO2] (eCO2) effect on the ecosystem's N balance and the whole-ecosystem stoichiometry, which, in turn, depends on the change in the C : N stoichiometry of vegetation and soil, as well as the partitioning of N between vegetation and soil (Rastetter et al., 1992).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4288990&req=5

fig01: Conceptual diagram of the major nitrogen (N) and carbon (C) flows and stores in a terrestrial ecosystem. Blue arrows denote C fluxes and red arrows N fluxes between major plant compartments (green) and soil pools (black). Numbers 1–5 mark important C–N cycle linkages as described in the Evaluation framework section: 1, N-based gross primary production (GPPN): the return of C assimilates per unit canopy N Eqn 1; 2, whole-plant nitrogen-use efficiency (NUE): the total amount of foliar, root and woody production per unit of N taken up by plants; this process depends on the allocation of growth between different plant compartments (e.g. leaves, fine roots and wood) and the C : N stoichiometry of each compartment Eqn 2; 3, plant N uptake (fNup): the capacity of the plants to take up N from the soil Eqn 4. The plant-available soil N is determined by two factors: 4, net N mineralization (fNmin): the amount of N liberated from organic material through decomposition, which varies with microbial activity and litter quality Eqn 6; and 5, the net ecosystem nitrogen exchange (NNE): based on N inputs from biological N fixation (fNfix) and atmospheric deposition (fNdep) and N losses from the ecosystem as a result of leaching to groundwater (fNleach) and gaseous emission (fNgas) Eqn 5. As an emergent property, the net amount of C that can be stored in an ecosystem following an increase in CO2 depends on the elevated atmospheric [CO2] (eCO2) effect on the ecosystem's N balance and the whole-ecosystem stoichiometry, which, in turn, depends on the change in the C : N stoichiometry of vegetation and soil, as well as the partitioning of N between vegetation and soil (Rastetter et al., 1992).
Mentions: Our study forms part of a model intercomparison (A. P. Walker et al., unpublished) looking at the effect of eCO2 on water (De Kauwe et al., 2013), C (M. G. De Kauwe et al., unpublished) and N cycling. Each of the participating models incorporates the major processes by which the N cycle affects the ecosystem's response to eCO2, such as plant N uptake, net N mineralization and the ecosystem N balance, as well as emergent ecosystem properties, such as the N-use efficiency (NUE) of plant production (Fig.1). The representation of these processes varies greatly among models (Table1), illustrating a lack of consensus on the nature of the mechanisms driving these processes. Our objectives in this study were as follows:

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Biogeochemical Integration Department, Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, D-07745, Jena, Germany.

Show MeSH
Related in: MedlinePlus