Ideas and perspectives: patterns of soil CO2, CH4, and N2O fluxes along an altitudinal gradient – a pilot study from an Ecuadorian neotropical montane forest

Lamprea Pineda, Paula Alejandra; Bauters, Marijn; Verbeeck, Hans; Baez, Selene; Barthel, Matti; Bodé, Samuel; Boeckx, Pascal

doi:https://doi.org/10.5194/bg-18-413-2021

Articles | Volume 18, issue 2

https://doi.org/10.5194/bg-18-413-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-18-413-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 2

Research article

|

19 Jan 2021

Research article |

| 19 Jan 2021

Ideas and perspectives: patterns of soil CO₂, CH₄, and N₂O fluxes along an altitudinal gradient – a pilot study from an Ecuadorian neotropical montane forest

Paula Alejandra Lamprea Pineda, Marijn Bauters, Hans Verbeeck, Selene Baez, Matti Barthel, Samuel Bodé, and Pascal Boeckx

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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: 'comments on Pineda et al', Klaus Butterbach-Bahl, 23 Apr 2020
- AC1: 'Response to reviewers', Paula Alejandra Lamprea Pineda, 29 Apr 2020
RC2: 'review bg-2020-105', Anonymous Referee #2, 24 Apr 2020
- AC2: 'Response to reviewers', Paula Alejandra Lamprea Pineda, 29 Apr 2020

Peer-review completion

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

ED: Reconsider after major revisions (05 Jun 2020) by Kees Jan van Groenigen

AR by Paula Alejandra Lamprea Pineda on behalf of the Authors (18 Jul 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (03 Aug 2020) by Kees Jan van Groenigen

RR by Klaus Butterbach-Bahl (20 Aug 2020)

Suggestions for revision or reasons for rejection

Dear authors,

thanks for the revision and restructuring of the manuscript. Looks more convincing to me now. I still find the discussion of results on soil CO2 fluxes highly speculative as no details on site, stand properties are provided. However, the point on N2O uptake, and the support of negative N2O flux data by evidence from isotopic signatures pointing towards N2O consumption is convincing and very interesting. I am surely supporting your lea for more research on tropical mountaineous forest ecosystems under climate change, but this might need to go alang as well with capacity building in the respective countries.

Here are a few additional points:
Line 37 while the argument is correct for CH4 and N2O, soil CO2 fluxes are highly dependent on root (autotrophic) respiration too. Revise sentence (and see your line 40 too).
Line 44 tropical forest soils
Line 46 Provide a reference for these numbers/ estimates of NEE
Line 57 I would suggest to include Table S1 in the main text
Lines 95-112 I find the discussion on the soil CO2 emissions extremely speculative as there is no information on vegetation biomass, root biomass, vegetation type etc. Given the acknowledged importance of root respiration and the known high temporal variability of soil respiration, and the missing stand information, I think that little can be learned out of this and would suggest to further shorten this part.
Line 115 just mention here the number of observations day
Line 139 check numbers for C_2200. If 20 fluxes should result in net emissions the range should have a positive value too
Line 144 typo with “-and”
Line 154-158 see also Denk et al. 2017, The nitrogen cycle: A review of isotope effects and isotope modelling approaches. Soil Biol. Biochem. 105, 121-137
Line 177 mention that root biomass was not measured nor estimated
Line 195-200 Possibly also mention the importance for capacity building on biogeochemistry and GHG research in the target regions. Given that these regions will be severely hit by climate change, but so far, knowledge mainly comes from outside, such a network approach would also be helpful to create a local knowledge base on how climate (and landuse change) might affect ecosystems (and people).

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RR by Anonymous Referee #3 (24 Sep 2020)

Suggestions for revision or reasons for rejection

This is an interesting work on soil GHG fluxes in an underrepresented region; it does not only provide a good (and short) dataset but also some insights into soil N2O uptake. I have had a look to the previous version and the comments of the reviewers and I agree with them that the experimental set up and the dataset fits better into a “preliminary data” paper. The paper is nicely and clearly written, and it is honest with regard to its limitations; at the same time, serves in suggesting ways forward for increasing our understanding on the patterns of GHG fluxes in tropical montane forest soils.
Probably one of the most relevant changes I suggest is with regard to the title. “Varying sources and sinks” seems to me that you look at different components within the forest, but this is not the case. I suggest to make explicit mention to the soil (e.g. –only a suggestion- “Ideas and perspectives: patterns of soil CO2, CH4 and N2O fluxes along ….”) and probably to montane forests.
Further, I understand the rationale of using GWP to compare between GHGs, but I strongly doubt the usefulness of including CO2 fluxes since, as you mentioned in the paper, it is only a part of the story and do not reflect inputs to the soil.
Finally, you highlight quite prominently the topographic position as a key driver controlling spatial variability (e.g. L32, L186); while this is true, other sources of variability may be equally important (e.g. degradation/forest management, hydrological status at the catchment level, soil types, exposition and associated microclimate) and should be taken into account when proposing “broader studies”.

For the rest, I only have a couple of minor comments, which are depicted below.

L41: Remove “(anaerobic)”
L44-46. I am missing a citation here, so I can´t check on my own. I guess this is the C sink of the forest, and not of the soil; since you previously referred to the soil, it is misleading, unless you are able to infer what proportion is stored in the vegetation and in the soil (or below- and aboveground).
L70: Probably merge the two paragraphs.
L75: Remove “more” before “severe”. Remove “even though forests can be managed to mitigate climate change as well”, it is not really relevant here. Eventually, you can state that it is important to understand the feedbacks to come up with appropriate forest management options to mitigate climate change.
L93: I suggest to change “budget” by “fluxes”.
L102: Zimmermann et al 2009(Eur J Soil Sci, doi: 10.1111/j.1365-2389.2009.01175.x) worked also on an altitudinal gradient in the Andes and pointed towards changing C allocation patterns. The paper might be also interesting for the summary table (I was not involved in this work).
L119: Remove “on the other hand”. Reformulate the second sentence. The lowest flux is the closest to 0, and this is not what you want to point out.
L139: The range is wrong, I think, it should go from negative to positive.
L143: This is also similar to what Gerschlauer (Biogeosciences) found in a gradient in the Kilimanjaro. I don´t remember if they found relationships between N2O fluxes and the isotopic signature in the soil, but may be worth looking at it (not involved either in the work).
L152: Probably “support” or similar, rather than “confirm”
L186: Remove “For instance”
L194: Why bi-weekly? To me, the sampling should cover seasonal fluctuations (dry vs. wet season), but also at a finer scale.
Fig 2: Note: “the dotted vertical line” instead of “the dotted x axis”
Fig 3: Even if the three GHG are represented using CO2-eq, consider an axe-break instead on the zoom-in view.

Table S1. This is a great compilation of information. However, I find difficult to compare the studies. I suggest to add more columns, in order to separate between measured and estimated annual, and also a field with comments/period of measurement). I also suggest not to use the publication as a basis, but the site (e.g. Garcia Montiel et al 2004 measured on different sites, so include a line for each, with the same reference). For me, manual and dynamic chambers are not mutually exclusive. Do you rather mean manual vs. automated? In any case, probably the frequency is more important than the method per se (e.g. manual chambers can have daily, or monthly frequency).

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ED: Publish subject to minor revisions (review by editor) (12 Oct 2020) by Kees Jan van Groenigen

AR by Paula Alejandra Lamprea Pineda on behalf of the Authors (24 Oct 2020) Manuscript

ED: Publish as is (27 Oct 2020) by Kees Jan van Groenigen

ED: Publish subject to minor revisions (review by editor) (05 Nov 2020) by Kees Jan van Groenigen

AR by Paula Alejandra Lamprea Pineda on behalf of the Authors (11 Nov 2020) Author's response Manuscript

ED: Publish as is (20 Nov 2020) by Kees Jan van Groenigen

AR by Paula Alejandra Lamprea Pineda on behalf of the Authors (23 Nov 2020) Author's response Manuscript

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Short summary

Tropical forest soils are an important source and sink of greenhouse gases (GHGs) with tropical montane forests having been poorly studied. In this pilot study, we explored soil fluxes of CO₂, CH₄, and N₂O in an Ecuadorian neotropical montane forest, where a net consumption of N₂O at higher altitudes was observed. Our results highlight the importance of short-term variations in N₂O and provide arguments and insights for future, more detailed studies on GHG fluxes from montane forest soils.