Carbon–nitrogen coupling under three schemes of model representation: a traceability analysis

Du, Zhenggang; Weng, Ensheng; Jiang, Lifen; Luo, Yiqi; Xia, Jianyang; Zhou, Xuhui

doi:https://doi.org/10.5194/gmd-11-4399-2018

Articles | Volume 11, issue 11

https://doi.org/10.5194/gmd-11-4399-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/gmd-11-4399-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 11, issue 11

Model evaluation paper

|

02 Nov 2018

Model evaluation paper |

| 02 Nov 2018

Carbon–nitrogen coupling under three schemes of model representation: a traceability analysis

Zhenggang Du, Ensheng Weng, Lifen Jiang, Yiqi Luo, Jianyang Xia, and Xuhui Zhou

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Final revised paper (published on 02 Nov 2018)
Supplement to the final revised paper
Preprint (discussion started on 15 Mar 2018)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Traceability analysis of terrestrial C-N model', Will Wieder, 16 Apr 2018
- AC1: 'Response letter to comments (gmd-2018-41)', Zhenggang Du, 02 Jul 2018
RC2: 'Comments to Du et al.', Anonymous Referee #2, 26 Apr 2018
- AC1: 'Response letter to comments (gmd-2018-41)', Zhenggang Du, 02 Jul 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Zhenggang Du on behalf of the Authors (02 Jul 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (08 Aug 2018) by Tomomichi Kato

RR by William Wieder (21 Aug 2018)

Suggestions for revision or reasons for rejection

I appreciate the revisions made to this manuscript. Two additional questions and several technical corrections arose after reading the text. I trust these can be addressed without too much trouble.

Why aren’t denitrification, or gaseous losses shown in Fig 3 or discussed with leaching losses (e.g. line 475)? Thomas et al. 2013 found big difference in the denitrification rates simulated by CLM4 and OC-N, so I'd assume at steady state the models make very different projections?

I’m not sure I completely understand the explanation ~ lines 530 and 558. It’s true, that CLM4.5 has fixed tissue stoichiometry, but it uses a dynamic C allocation scheme that should modify the C allocation to wood, stoichiometry, and MRT (at least in transient simulations)? This would also affect the allocation to wood vs. fine roots during spinup, with proportionally less wood C allocation associated with lower NPP? Are these nuances of C allocation from SM2 & 3 brought into the TECO simulations presented? If not, maybe this is more of a nuance of how the sensitivities were calculated, but perhaps worth clarifying?

Technical corrections
L 85: should be ‘dynamics’

L 103: I’m not really sure what “achieved predictive ability” means? Maybe delete this entire clause after the end of the parenthesis in line 102

L 109: are references needed for these models, as well as a description of their abbreviated names?

L 153: it seems to introduce talk about “plant, litter and soil N pools” immediately following mention of the inorganic N pool. Consider revising “There are nine organic N pools - including plant, litter and soil N pools - and one inorganic soil N pool”.

Eq 20 & Line 463, Maybe worth citing Cleveland et al 1999, which is the source of this CLM4.5 approach for BNF (and I’m assuming for O-CN).

L 350, why not convert to mg N m^-2 d^-1 so the values are intelligible? Also, is the daily variation important here, or the total flux calculated by each model? My guess is both, but the latter is never really described (although it’s displayed in the right column of Fig 3)?

L 353 & 354, no daily variation for leaching or Nfix is reported here?

L 370 & Fig 4, how does one generate a positive NEE for all years in all model configurations if steady state conditions were achieved before starting the transient simulation? By definition, it seems NEE should be zero over the years the correspond the equilibrium conditions? I don’t understand how / or why a NSC pool would affect the calculation of NEE, is the model just storing up NSC?

Fig 5,would it make more sense to plot both panels with a log y axis to show variation in bools and stoichiometry?

Line 414 and 416, what to b2 and b3 refer to? Is this eq 2 & 3, if so maybe refer to these equations instead?

L 452, isn’t thus just Jmax in the Farquhar model (not Vjmax)?

L 538, is this more specifically related to vegetation C:N ratio (not total)

References:
Cleveland, C. C., et al. (1999), Global patterns of terrestrial biological nitrogen (N2) fixation in natural ecosystems, Global Biogeochem. Cycles, 13(2), 623–645, doi: 10.1029/1999GB900014.

Thomas et al. (2013) Global patterns of nitrogen limitation: confronting two global biogeochemical models with observations Global Change Biology 19, 2986–2998, doi: 10.1111/gcb.12281

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RR by Anonymous Referee #2 (13 Sep 2018)

ED: Publish subject to minor revisions (review by editor) (13 Sep 2018) by Tomomichi Kato

AR by Zhenggang Du on behalf of the Authors (22 Sep 2018) Author's response

ED: Publish as is (11 Oct 2018) by Tomomichi Kato

AR by Zhenggang Du on behalf of the Authors (17 Oct 2018)

Short summary

In this study, based on a traceability analysis technique, we evaluated alternative representations of C–N interactions and their impacts on the C cycle using the TECO model framework. Our results showed that different representations of C–N coupling processes lead to divergent effects on plant production, C residence time, and thus the ecosystem C storage capacity. Identifying those effects can help us to improve the N limitation assumptions employed in terrestrial ecosystem models.