Stomatal control of leaf fluxes of carbonyl sulfide and CO<sub>2</sub> in a <i>Typha</i> freshwater marsh

Sun, Wu; Maseyk, Kadmiel; Lett, Céline; Seibt, Ulli

doi:https://doi.org/10.5194/bg-15-3277-2018

Articles | Volume 15, issue 11

https://doi.org/10.5194/bg-15-3277-2018

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

https://doi.org/10.5194/bg-15-3277-2018

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

Articles | Volume 15, issue 11

Research article

|

04 Jun 2018

Research article |

| 04 Jun 2018

Stomatal control of leaf fluxes of carbonyl sulfide and CO₂ in a Typha freshwater marsh

Wu Sun, Kadmiel Maseyk, Céline Lett, and Ulli Seibt

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Final revised paper (published on 04 Jun 2018)
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Preprint (discussion started on 07 Nov 2017)

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

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RC1: 'Interesting and relevant findings more suitable for a technical note than for a regular research paper', Teresa Gimeno, 15 Nov 2017
- AC1: 'Response to reviewer #1's comments', Wu Sun, 08 Mar 2018
SC1: 'Clarifications of the chamber system, stomatal conductance data, and LRU', Wu Sun, 18 Nov 2017
RC2: 'Good dataset; please rework interpretation', M.E. Whelan, 03 Jan 2018
- AC1: 'Response to reviewer #1's comments', Wu Sun, 08 Mar 2018

Peer-review completion

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

ED: Reconsider after major revisions (14 Mar 2018) by Paul Stoy

AR by Wu Sun on behalf of the Authors (20 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 Mar 2018) by Paul Stoy

RR by Teresa Gimeno (26 Mar 2018)

Suggestions for revision or reasons for rejection

This is the second time I review this manuscript and I would like to highlight again the clarity of the text and the presentation of the results. I believe this manuscript has improved significantly with respect to its previous version. The theoretical framing of the study is more solid, I really appreciated the author’s effort to formulate two specific hypotheses. I have some comments on that regard that I detail below. The technical clarifications added are pertinent and specific and I only have a few minor questions (again see below). I think the addition of the detailed explanation of the calculations underlying the different diffusion components and the inclusion of the stomatal conductance was needed. The discussion has vastly improved with respect to the previous version, being a lot more interesting and better suited to the results presented.

My biggest concern is still related to the limited scope of the paper. The authors need to acknowledge the limitations of their study clearly. As they stated in the response letter themselves, replication is always desirable in any study and although any potential reader (as well I myself or the handling editor) would recognise the technical and practical limitations of any field study, these limitations need to be stated clearly. The main limitation of this study is that only one set of six leaves (from the same plant?) was measured continuously and that the target species is a bit particular in terms of physiological behaviour. This study focuses on a salt-marsh plant, which undoubtedly serves as an excellent target for a proof-of-concept type study. However, it should be noted that the observed results might be influenced by its particular physiology and habitat preference, as noted on the comments to the previous version by Dr M. E. Whelan and myself. Besides, it appears that these leaves might not necessarily be the most representative as “the chamber received slightly more light in the afternoon than in the morning due to a wider gap in the canopy to the west of the chamber than to other directions” (P10L9). I am not saying that these circumstances ought to be a weakness, but CO2 and COS patterns could have coupled differently under different circumstances, and this is an important limitation that needs to be acknowledged very early in the discussion.

All my comments below refer to the page and line numbers (PXLY) on the manuscript version with the track changes where insertions and deletions with respect to the previous version were indicated.

P3L11 Please correct me if I am wrong, but I believe that there is not “only one study reporting nighttime COS uptake at the leaf scale” since besides Berkelhammer et al. (Global Biogeochemical Cycles, 28, 161–179, 2014), Koojimans et al. (Atmos. Chem. Phys., 17, 11453–11465, 2017) also report chamber-level measurements of nocturnal COS uptake in the field and Stimler et al. (New Phytologist, 186, 869-878, 2010) report leaf level COS uptake under laboratory conditions in the dark. I believe the authors might want to consider rephrasing this statement and/or adding some citations.

P3L20-P4L9 In my opinion, and in line with the previous comments raised by Dr M. E. Wehelan, I believe the manuscript would benefit greatly from reducing the emphasis on the relevance of LRU. This paragraph provides a nice review of previously reported responses of LRU to environmental drivers, but it would be more appropriate to reduce it to one or two sentences targeted at formulating the study hypotheses at the relevant scale (leaf).

P4L12 I really appreciated the author’s effort to formulate specific hypotheses; nevertheless, I do not follow what information given on the introduction leads to formulating hypothesis (ii). I think this needs to be clarified.

P5L10 How was leaf area ‘estimated’?

Remove “reaffirming the shared stomatal control on both fluxes” (P11L23-25, on the top), also “This indicates that stomatal conductance exerted a stronger control on COS uptake than CO2 uptake” (P11L6-7) and “This difference may be attributed to changes in internal conductance terms entailed in gtot, COS, namely, mesophyll conductance and biochemical activities.” (P11L16-17). Speculations and suggestions on which processes underlie these correlations and patterns belongs to the discussion.

P11L20 I am not sure I understand how Figure 6b illustrates how stomata opening limited COS diffusion more strongly than for CO2 since the 25-75th percentile intervals appear to overlap completely for these two gases. I would like to ask the authors to consider rephrasing or even removing this statement, or maybe to accompany with some sort of formal statistical test.

P12L12-13 In agreement with my previous comments, I consider that this [“when the difference between stomatal limitation…”] could be viewed as an over-interpretation of the observed patterns.

P12L19 Could you please provide the P-value for this correlation?

P12L21-22 I would move the last part of this paragraph [“similar to (…) the daily timescale”] to the discussion.

P12L24 I agree that stomatal and other internal diffusion resistances (which are not accounted for here) are likely to underlie the observed patters of COS and CO2 uptake measured here. Nevertheless, maybe the authors should consider opening their discussion by briefly reminding the reader whether their results agree with their original hypotheses. In addition, I think it is very important to state here, very clearly, the limitations of the study, mainly that observations are limited to one single set of leaves in a salt marsh plant, which has a very particular physiology. In the previous review, both Dr. M. E. Whelan and myself noted several particularities of the physiology of this plant and these need to be incorporated in the discussion as they might influence the coupling of COS and CO2 fluxes and their underlying regulation by stomatal conductance.

Figure 4. I understand that the correlation coefficient (r2) from figure (a) corresponds to a linear fit between leaf CO2 and COS fluxes, but I cannot see what would be the equivalent fit in (b). This needs to be clarified in the figure legend. Also, please consider providing P-values here too.

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RR by Anonymous Referee #3 (26 Apr 2018)

ED: Publish subject to minor revisions (review by editor) (27 Apr 2018) by Paul Stoy

AR by Wu Sun on behalf of the Authors (15 May 2018) Author's response Manuscript

ED: Publish as is (19 May 2018) by Paul Stoy

AR by Wu Sun on behalf of the Authors (20 May 2018)

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Short summary

Carbonyl sulfide (COS) is an emerging tracer to probe land photosynthesis at canopy to global scales, but the relationship between leaf COS and CO₂ fluxes needed for this application is poorly quantified. With in situ leaf fluxes of COS and CO₂ measured in a freshwater marsh, we show that light and vapor deficit control the relationship between leaf COS and CO₂ fluxes by regulating stomatal conductance. Our findings support the use of COS as a tracer for canopy photosynthesis.

Stomatal control of leaf fluxes of carbonyl sulfide and CO2 in a Typha freshwater marsh

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Interactive discussion

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Stomatal control of leaf fluxes of carbonyl sulfide and CO₂ in a Typha freshwater marsh