Limits...
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.

Show MeSH
First year response of nitrogen (N)-based net primary production (NPPN) to elevated atmospheric [CO2] (eCO2) (a, b) and the change between the first year and the final 5 yr of the experiment (c, d) at the Duke and Oak Ridge National Laboratory (ORNL) Free-Air CO2 Enrichment (FACE) sites, respectively, as well as the response of plant carbon (C)-use efficiency (CUE), N-based gross primary production (GPPN) and canopy N, expressed as total canopy N (Ncan) and foliar N concentration (ncan). The grey boxes denote the mean observed eCO2 response ± 1SE, where observations corresponding to model output are available.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4288990&req=5

fig06: First year response of nitrogen (N)-based net primary production (NPPN) to elevated atmospheric [CO2] (eCO2) (a, b) and the change between the first year and the final 5 yr of the experiment (c, d) at the Duke and Oak Ridge National Laboratory (ORNL) Free-Air CO2 Enrichment (FACE) sites, respectively, as well as the response of plant carbon (C)-use efficiency (CUE), N-based gross primary production (GPPN) and canopy N, expressed as total canopy N (Ncan) and foliar N concentration (ncan). The grey boxes denote the mean observed eCO2 response ± 1SE, where observations corresponding to model output are available.

Mentions: Models differed strongly in their initial NPPN response to eCO2 (Fig.6), generally overestimating the observed initial 11 ± 8% increase in NPPN at Duke FACE and underestimating the observed 35 ± 4% increase at ORNL FACE. Although N limitation did not strongly affect GPPN in the first year in most models, there were substantial differences in the first year's response among the models, in particular at ORNL FACE. Two models (CABLE and CLM4) showed an exceptionally low initial response of NPP at both sites (Fig.5). This low response was related to a near-zero response of GPPN (Fig.6a,b). In CLM4, this response resulted from the assumption that plants down-regulate GPP directly when N limited: CO2 fertilization of GPP is calculated in the absence of N limitation, and then reduced using N-limitation scalars if fNup is insufficient to support this amount of productivity. This low response did not happen in other models that followed a similar approach (DAYCENT and ED2.1), because of sufficient initial N supply. Another class of models simulated photosynthesis based on foliar N content (CABLE, GDAY, LPJ-GUESS, OCN, SDGVM, TECO). In these models, N limitation on GPP acts via foliar N concentrations: limited N availability reduces foliage N, which feeds back to limit GPP. This limitation takes time to develop, such that it was absent or weak in the initial response, but with a strong component of down-regulation in the longer term (Fig.6c,d).


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)

First year response of nitrogen (N)-based net primary production (NPPN) to elevated atmospheric [CO2] (eCO2) (a, b) and the change between the first year and the final 5 yr of the experiment (c, d) at the Duke and Oak Ridge National Laboratory (ORNL) Free-Air CO2 Enrichment (FACE) sites, respectively, as well as the response of plant carbon (C)-use efficiency (CUE), N-based gross primary production (GPPN) and canopy N, expressed as total canopy N (Ncan) and foliar N concentration (ncan). The grey boxes denote the mean observed eCO2 response ± 1SE, where observations corresponding to model output are available.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig06: First year response of nitrogen (N)-based net primary production (NPPN) to elevated atmospheric [CO2] (eCO2) (a, b) and the change between the first year and the final 5 yr of the experiment (c, d) at the Duke and Oak Ridge National Laboratory (ORNL) Free-Air CO2 Enrichment (FACE) sites, respectively, as well as the response of plant carbon (C)-use efficiency (CUE), N-based gross primary production (GPPN) and canopy N, expressed as total canopy N (Ncan) and foliar N concentration (ncan). The grey boxes denote the mean observed eCO2 response ± 1SE, where observations corresponding to model output are available.
Mentions: Models differed strongly in their initial NPPN response to eCO2 (Fig.6), generally overestimating the observed initial 11 ± 8% increase in NPPN at Duke FACE and underestimating the observed 35 ± 4% increase at ORNL FACE. Although N limitation did not strongly affect GPPN in the first year in most models, there were substantial differences in the first year's response among the models, in particular at ORNL FACE. Two models (CABLE and CLM4) showed an exceptionally low initial response of NPP at both sites (Fig.5). This low response was related to a near-zero response of GPPN (Fig.6a,b). In CLM4, this response resulted from the assumption that plants down-regulate GPP directly when N limited: CO2 fertilization of GPP is calculated in the absence of N limitation, and then reduced using N-limitation scalars if fNup is insufficient to support this amount of productivity. This low response did not happen in other models that followed a similar approach (DAYCENT and ED2.1), because of sufficient initial N supply. Another class of models simulated photosynthesis based on foliar N content (CABLE, GDAY, LPJ-GUESS, OCN, SDGVM, TECO). In these models, N limitation on GPP acts via foliar N concentrations: limited N availability reduces foliage N, which feeds back to limit GPP. This limitation takes time to develop, such that it was absent or weak in the initial response, but with a strong component of down-regulation in the longer term (Fig.6c,d).

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