Wintertime grassland dynamics may influence belowground biomass under climate change: a model analysis

Katata, Genki; Grote, Rüdiger; Mauder, Matthias; Zeeman, Matthias J.; Ota, Masakazu

doi:https://doi.org/10.5194/bg-17-1071-2020

Articles | Volume 17, issue 4

https://doi.org/10.5194/bg-17-1071-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-17-1071-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 4

Research article

|

28 Feb 2020

Research article |

| 28 Feb 2020

Wintertime grassland dynamics may influence belowground biomass under climate change: a model analysis

Genki Katata, Rüdiger Grote, Matthias Mauder, Matthias J. Zeeman, and Masakazu Ota

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Final revised paper (published on 28 Feb 2020)
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Preprint (discussion started on 04 Sep 2019)
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Interactive discussion

Status: closed

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

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RC1: 'Review of Katata et al. manuscript', Anonymous Referee #1, 09 Oct 2019
- AC1: 'Response to Anonymous Referee #1', Genki Katata, 09 Nov 2019
RC2: 'Referee Comment to Wintertime carbon uptake...', Anonymous Referee #2, 11 Oct 2019
- AC2: 'Response to Anonymous Referee #2', Genki Katata, 09 Nov 2019

Peer-review completion

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

ED: Reconsider after major revisions (14 Nov 2019) by Paul Stoy

AR by Genki Katata on behalf of the Authors (18 Nov 2019) Manuscript

ED: Referee Nomination & Report Request started (25 Nov 2019) by Paul Stoy

RR by Anonymous Referee #2 (11 Dec 2019)

Suggestions for revision or reasons for rejection

‘Wintertime carbon uptake of managed temperate grassland ecosystems may influence grassland dynamics’ – the influence of reduced snowcover and its effects on carbon uptake was already analyzed based on the same data that is presented here in Zeeman et al 2017. Although the current study focuses more on model development and simulations and the data is only used for model validation, I still think what you present is not substantially new or innovative. In response to my review comment you write that uncovering long-term effects due to seasonal variations in carbon allocation is your main intention. However, this is not clear from the title and there is no straightforward introduction. Moreover, from the results you present you are drawing inconsistent and unsupported conclusions. For example, you write in L 212 ‘differences between scenarios were small for all variables at the Grasswang site’. The new Figure 6, however, shows that the relative increase of GPP for the active scenario compared to the dormant scenario is probably of the same order of magnitude at the Graswang site than at Fendt. That the absolute numbers are smaller can most likely be attributed to the fact, that Graswang is at an higher altitude and therefore has lower temperatures and more snowcover even during the warm winter. And on the other hand, if the differences between the different scenarios indeed are not significant, then your argument that calibrated values for Tph for each site are necessary is lapsed since the one that fits best for Fendt apparently fits for Grasweng well enough. Moreover, I do not agree with your conclusion, that ‘a large fraction of carbon (CO2) gained by photosynthesis during winter was […] used to grow roots during the spring growth period’ (L 263ff). Neither the dormant nor the active scenario in Fendt as well as in Graswang show an increase in the reserve content during winter (the active scenario even shows a reduction), so there is no carbon stored during winter that can be used for root growth? Moreover, the increased root biomass in spring in the active scenario can also be observed in Graswang, although you argue previously that there is no relevant photosynthesis during winter.
Indeed it is interesting to see, that the above ground biomass is almost the same at the first cutting for both scenarios. However, it seems like the rate of biomass gain at the beginning of spring is very high and about the same for both scenarios but levels off later indicating that a possible maximum is reached in both cases (e.g. no further increase due to light limitation when the canopy gets too dense). This could possibly be analyzed in more detail with different model scenarios…

If you want to improve and re-submit the manuscript I recommend as previously mentioned to carefully evaluate the underlying processes of the model and validate they actually present the ‘true’ ecosystem processes. Analyze the model output carefully and make sure your conclusions are consistent and that there is a clear central theme from the title, introduction, results to the discussion and conclusions.

Make sure to cite the original papers. For example, you write: “but growth stops if soil temperatures are lower than 5 ◦C (Körner, 2008). […] In this situation, organic matter (organic carbon) produced by photosynthesis is not used for grass growth but accumulates in the plant as reserves during winter (e.g., Körner, 2008).” But Körner 2008 mentions the 5 °C limit and that organic matter accumulates in reserves, but this is not the original research and he refers to other papers.

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ED: Reconsider after major revisions (12 Dec 2019) by Paul Stoy

AR by Genki Katata on behalf of the Authors (15 Jan 2020) Manuscript

ED: Publish as is (23 Jan 2020) by Paul Stoy

AR by Genki Katata on behalf of the Authors (24 Jan 2020) Manuscript

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Short summary

In this paper, we demonstrate that high physiological activity levels during the extremely warm winter are allocated into the below-ground biomass and only to a minor extent used for additional plant growth during early spring. This process is so far largely unaccounted for in scenario analysis using global terrestrial biosphere models, and it may lead to carbon accumulation in the soil and/or carbon loss from the soil as a response to global warming.