the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Nov 2024
Reviews and syntheses: Contribution of sulfate to methane oxidation in upland soils: a mini-review
Abstract. Methane (CH4) is a potent greenhouse gas, its global warming potential is 25 times higher than carbon dioxide (CO2), and various environmental factors influence CH4 oxidation in soil. Sulfate (SO42-) ion is the main component of atmospheric deposition and has been increasing in recent years, it promotes CH4 production and anaerobic CH4 oxidation, however, the impact of SO42- on CH4 oxidation remains inconclusive. Due to the limited research on the effects of SO42- on CH4 oxidation, we synthesize current research on the effects of SO42- on CH4 oxidation, examining both its direct impact and its influence on the dynamics of soil substances, and the potential indirect effects of SO42- on CH4 oxidation. Through a literature review, we identified that SO42- facilitates CH4 oxidation within a range of 3–42 %, moreover, it has been found that various physicochemical properties and processes in the soil are influenced by the addition of SO42-, which in turn affects CH4 oxidation. This review enhances our understanding of the role of SO42- in promoting CH4 oxidation and lays the foundation for future studies aimed at validating these findings by quantifying CH4 flux and oxidation rates, as well as elucidating the underlying microbial processes via experimental research. This review deepens the comprehension of atmospheric CH4 flux and the global CH4 cycle, particularly in the context of potential global environmental changes.
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Status: open (until 10 Jan 2025)
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CC1: 'Comment on egusphere-2024-3347', Yongchuan Yang, 02 Jan 2025
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Hello author, I have a question to ask you. Why did you think of sorting out the relationship between sulfate ions and methane oxidation？
Citation: https://doi.org/10.5194/egusphere-2024-3347-CC1 -
AC1: 'Reply on CC1', lihua zhang, 04 Jan 2025
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Thank you for your comment. I would like to clarify our investigation into the relationship between SO42- and CH4 oxidation. First, previous studies have shown that SO42- promotes the anaerobic oxidation of CH4, as SO42- serves as an electron acceptor in this process. Second, SO42- inhibits CH4 production primarily due to its thermodynamic and kinetic preference as an electron acceptor. Third, based on above two key processes in the CH4 cycle being influenced by SO42-, we hypothesize that SO42- might also affect CH₄ oxidation, a process that has been shown to be promoted by SO42- in some studies. Thus, we aim to clarify the relationship between SO42- and CH4 oxidation, as well as potential connections, through this review, providing a foundation for future experiments on the impact of SO42- on CH4 oxidation. Finally, we have conducted indoor incubation experiments that confirm SO42- does indeed influence CH4 oxidation and promotes it. We are currently writing up the results of these experiments and plan to publish them soon, which will further support the findings presented in this review. These are my answers and I hope they clear up your doubts.
Citation: https://doi.org/10.5194/egusphere-2024-3347-AC1
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AC1: 'Reply on CC1', lihua zhang, 04 Jan 2025
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RC1: 'Comment on egusphere-2024-3347', Anonymous Referee #1, 02 Jan 2025
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The authors aimed to review on direct and indirect contributions of sulfate to methane oxidation in upland soils. As far as I’m concerned, influence of sulfate on methane oxidation is an important topic in biogeochemistry, but the current manuscript failed to make a clear and concise presentation. Here I list my major concerns as follows.
1) Methane oxidation or aerobic methane oxidation?
The manuscript is entitled ‘Contribution of sulfate to methane oxidation...’, but throughout the manuscript the authors seemed to talk only about aerobic methane oxidation. Note that both aerobic and anaerobic methane oxidation exist in upland soils. If the authors just want to review on aerobic methane oxidation processes, please change the title into ‘…Contribution of sulfate to aerobic methane oxidation…’. If not, previous studies regarding anaerobic methane oxidation should also be reviewed in the manuscript.
2) Direct effects?
The authors stated that ‘This review provides a comprehensive summary of the direct and potential indirect impacts of SO42- on CH4 oxidation’ (L. 82 - 84), but I cannot see how sulfate directly influences methane oxidation in the manuscript. It seems that the authors tried to figure out the direct effect in the third part of the manuscript (L. 186 – 250), but they only concluded that ‘due to the scarcity of studies investigating the direct effect of SO42- on CH4 oxidation, no definitive conclusion regarding its impact could be drawn’ (L. 245 - 247).
Before discussing direct impacts of sulfate on methane oxidation, the authors should first answer whether sulfate could directly influence methane oxidation. Unfortunately, the authors didn’t even try to demonstrate existence of direct influence of sulfate on methane oxidation, but they made a conclusion that they provided ‘a comprehensive summary of the direct and potential indirect impacts’. Therefore, I think the conclusion regarding direct impacts should be modified throughout the manuscript.
From my perspective, direct effects of sulfate on methane oxidation is associated with coupling of anaerobic methane oxidation to sulfate reduction. Under anoxic conditions, numerous studies have demonstrated that sulfate could be the electron acceptor for methane oxidation, which can be considered a direct effect of sulfate on methane oxidation. However, the authors didn’t review on aerobic methane oxidation in the current manuscript.
3) Concerns regarding the major conclusion
From table 1, the authors drew the conclusion that ‘the enhancement of SO42- on CH4 oxidation is prominent in numerous studies’ (L. 74) and that ‘SO42- facilitates CH4 oxidation within a range of 3-42%’ (L. 75). However, table 1 only contains results from 5 study sites, and no effect of sulfate addition was observed in 2 out of the 5 sites. In the 5 sites, effects of sulfate addition are 0%, 0%, 3%, 25% and 42%, respectively, and no statistical analysis has been conducted to support the statement that sulfate facilitate methane oxidation by 3-42%. Therefore, I think this conclusion is greatly undermined because of insufficient literature and lack of effective statistics. Additionally, title of table 1 is ‘Promotion effect of sulfate on methane oxidation in diverse biome soils’, but I don’t think 5 forests could be called “diverse biome”.
4) Concerns regarding manuscript structure
I also have some concerns regarding structure of the manuscript. First, the authors spent 2 pages introducing the methane oxidation processes and associated microbes (Pages 4 - 5), which are not much associated with the main topic of the manuscript. These contents are not reviewed in the following parts, and I suggest the authors to shorten these contents. Second, Lines 174 – 182 in section 2.3 repeated contents in the introduction (Lines 60 - 68). Similar sentences also emerged in the implication section (Lines 355 - 360). Third, contents in section 3 are disorganized, and I suggest the authors to reorganize these contents (e. g. by adding a topic sentence to the beginning of each paragraph of this section). Forth, presentation of table 1 (L. 75 - 78) should be in the result section (e.g. section 3), instead of the introduction.
Minor points:
- Omission of conjunctions. Grammatically, clauses should be joined by conjunctions, but conjunctions in many places are omitted in the manuscript, especially in the abstract. For example, Lines 16, 20, 21 and 26.
- There should be no line feed in ‘Norway Scots Pine forest’ in Table 1 (the first column, the forth row).
Citation: https://doi.org/10.5194/egusphere-2024-3347-RC1
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