Review Reports - Beyond Invasion: How <i>Phragmites australis</i> Modifies Soil Architecture and Carbon Storage in Long Island Sound Salt Marshes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study evaluates how invasion by Phragmites australis alters soil physical structure and carbon storage dynamics in Long Island Sound salt marshes, revealing a tradeoff between increased soil density and potential resilience to sea-level rise and greater spatial heterogeneity in carbon sequestration compared to native Spartina alterniflora. The manuscript contains good information; the current state of research in the field is well presented and well-integrated in the article. Several issues remain that require attention.

Comments for author File: Comments.pdf

Author Response

Thank you for these constructive comments – our responses are provided below in bold

I appreciate the aim of the study, but several issues remain that require attention before the article is suitable for publication.

The title can be improved, if possible to replace `may`.

Thank you for this suggestion. While the evidence for densely packed soils (significantly greater bulk density) is irrefutable in our dataset, it only implies increased protection which is why we feel the word “may” needs to be included.

Simple Summary and Abstract can be merged in one more concise section, as a concise, standalone summary of a scientific study that briefly presents the background, objectives, methods, key results, and main conclusions.

Noted, we included the simple summary as part of the formatting template we received but can delete if not needed.

Introduction. We recommend explicitly framing coastal salt marshes within the `blue carbon` concept, defined as the long-term sequestration of atmospheric carbon in coastal and marine ecosystems such as salt marshes, mangroves, and seagrasses, and distinguishing it from `green carbon` stored in terrestrial forests and soils by emphasizing the dominant role of waterlogged sediments and long-term burial in blue carbon systems.

We included a sentence that clarifies how salt marshes sequester carbon through waterlogging as other blue carbon systems.

The author must use/mention the current name for Spartina alterniflora =

Sporobolus alterniflorus (Loisel.) P.M.Peterson & Saarela

In the introduction, we mention the current name Sporobolus alterniflorus, throughout the document but mention the older name Spartina alterniflora for continuity.

In Introduction, please state the objective of the study. Authors are advised to clearly state the aim of the study and formulate the main proposed questions.

We included objectives at the end of the introduction.

Materials and Methods.

Use space before units, ex. °C – lines 105-111, 153, cm – line 157, and use correct symbol for oC (lines 152, 197). These were corrected

Line 144. masl – must be m a.s.l. and insert this abbreviation in the same line at: meters above sea level (m a.s.l.). This was added and corrected.

If author intend to include Ewbank (2017) in reference list, they should Check the original source document where the citation first appears to find the full reference details (title, institution, report number, publisher). If this is a grey literature report (e.g., agency or consultant report), format it accordingly (with author/organization, year, full title, location, and any report number). Verify the spelling of the author’s name and the correct year before finalizing the citation.

The reference to Ewbank (2017) was to a news article. We decided to remove is because the observation of vegetation composition was easily made (the preserve is quite small and easy to walk around) while on site and there is no need for a reference.

Also, the sentence ”The Quinnipiac Meadows site vegetation is comprised of S. alterniflora and P. australis backed by coastal Forest” (lines 123-125) refers to the vegetation composition and

spatial arrangement of the Quinnipiac Meadows site. Specifically, it can be improved to clarify that at the Quinnipiac Meadows site, the marsh vegetation is dominated by Spartina alterniflora and Phragmites australis, and these marsh communities are located adjacent to (or landward of) a coastal forest. In other words, S. alterniflora and P. australis occupy the marsh zone, while a coastal forest forms the upland boundary behind the marsh.

We substituted the original sentence with this one – “At Quinnipiac Meadows, the marsh is dominated by S. alterniflorus and P. australis backed by coastal forest.”

Results.

The statement “Above-ground biomass was greater in Phragmites in 2023 but lower in 2024” requires further elaboration and contextualization. The authors are encouraged to expand the discussion to better explain the contrasting interannual pattern observed. In particular, possible drivers of the higher biomass in 2023 should be explored, such as favorable climatic conditions (e.g., temperature, precipitation), nutrient availability, hydrological regime, or reduced disturbance during the growing season. Conversely, the lower biomass recorded in 2024 warrants discussion of potential stressors, including drought, flooding, management interventions, phenological shifts, or density-dependent effects following high biomass production in the previous year. Additionally, the authors should consider whether legacy effects of the exceptionally high biomass in 2023 (e.g., resource depletion, self-shading, or litter accumulation) may have contributed to reduced growth in 2024. Comparing these findings with similar interannual variability reported in other studies on Phragmites would strengthen the interpretation and help determine whether the observed pattern reflects local conditions or broader ecological trends. Overall, expanding the explanation of these results and integrating them into a broader ecological and management context would substantially improve the clarity and scientific relevance of the discussion.

We agree that an explanation is warranted. At Branford, we found that Phragmites was consistently taller than Spartina, however, the plants were less dense. Therefore we propose a possible reason for this change. Phragmites is a cosmopolitan species that thrives in both temperate and tropical climates. A shift in climate may not have a strong impact on this highly adaptable species,. We suspect the lower biomass in 2023 could be the result of mowing We had no way of knowing if the mowing took place prior to collection in 2023, however, we observed mowing in 2025. Fast growth of Phragmites could account for taller plants, but the disturbance could have had long lasting impacts. In 2024, we suspect that the plants had continued to grow for some time, allowing them to surpass Spartina.

On the other hand, the reduced biomass of Spartina from 2023 to 2024 at the same location could reflect the plants response to weather. Spartina thrives in moderate precipitation and temperature and suffers under extreme events such as drought or flooding. The summer of 2023 saw near normal weather conditions whereas 2024 was marked by much higher temperature and precipitation. Both of which could have negatively impacted Spartina growth.

However, in order to minimize distractions from the objectives of the study we chose to eliminate the discussion and results pertaining to above-ground biomass and instead focus on inferring how above ground biomass can impact soil carbon in the discussion.

In Tables 1&2, in column for species is mentioned only genera.

We changed this to reflect the Genera initial and species full name as in the text.

Discussion.

Author can insert discussion regarding the above-ground biomass production, and compare it with other studies (ex. Windham, L., & Lathrop, R. G. (1999). Effects of Phragmites australis invasion on aboveground biomass and soil properties in brackish tidal marsh of the Mullica River, New Jersey. Estuaries, 22(4), 927–935.)

We included a discussion section related to Eller 2016 and Hanson (2017) which specifically address the effects of climate and disturbance on plant growth and subsequently carbon accumulation in soils. We also included a reference to Windham and Lathrop (1999) to support the disturbance hypothesis when compared to other locations.

Several interpretations would benefit from clearer differentiation between observed results and inferred mechanisms. In particular, statements regarding sediment trapping, substrate compaction, and platform “hardening” could be framed more cautiously to avoid implying direct causality where only correlative evidence is available. Using more conditional language (e.g., “suggests,” “may indicate,” “is consistent with”) would strengthen the scientific rigor of these interpretations.

Thank you for this suggestion, we rephrased the statements to include more conservative, suggestive language which is more in line with the scope of the study.

The role of site-specific environmental drivers is appropriately acknowledged, but their influence could be more tightly integrated into the interpretation of results. Explicitly linking findings to the hydrological regime, sediment supply, and nutrient loading characteristics of the Long Island Sound would clarify the extent to which the observed patterns are locally driven versus broadly generalizable. This distinction is particularly important when discussing carbon storage dynamics and soil structural variability.

We worked to summarize the role of environmental drivers more succinctly particularly climate and hydrology which could influence growth and carbon storage.

Sections addressing nutrient enrichment and resilience to sea-level rise offer compelling insights but verge on normative interpretations regarding the functional advantages of P. australis. These sections would benefit from a more balanced discussion of ecological trade-offs, including potential consequences for biodiversity, habitat structure, and trophic interactions. Framing P. australis as functionally different rather than universally superior would reduce the risk of oversimplified management implications.

Finally, the Discussion would be strengthened by the inclusion of a brief integrative concluding paragraph synthesizing geomorphic engineering, carbon storage, nutrient dynamics, and sea-level rise resilience. Such a synthesis would reinforce the central message that invasion by P. australis represents a shift in ecosystem function and physical structure, rather than a unidirectional gain or loss in ecosystem services.

Although the comparison between Phragmites australis and Spartina alterniflora is implicit throughout the Discussion, it would benefit from more explicit, side-by-side contrasts. In several instances, P. australis dominates the narrative, while S. alterniflora serves mainly as a reference point. More direct comparative statements highlighting functional tradeoffs (such as uniformity versus heterogeneity or biotic stability versus physical resilience), would strengthen the comparative framework.

We appreciate this observation. In the discussion, we sought to enhance the balance by including statements such as “Despite the suggested geomorphic advantages of the establishment of non-native P. australis, it comes with significant ecological trade-offs. The tendency of P. australis to form dense, near-monocultural stands simplifies habitat structure, potentially reduc-ing biodiversity and altering trophic pathways for native avian and macroinvertebrate communities (Meyerson et al., 2000; Hunter et al., 2006). Thus, the invasion represents a transition from the biological heterogeneity and specialized habitat niches of S. alterniflorus to a more physically stable but biologically uniform state. “ and again in the conclusion “However, this shift involves a clear trade-off between the biotic stability and high-quality habitat provided by native S. alterniflorus.”

Ex. Line 64, 69. Spartina alterniflora, P. australis – italic (verify entire manuscript)

We ensured all species name mentions are italicized throughout.

Ex. Line 81 - Spartina spp. = Spartina spp. (italic, scientific names)

References – the DOI numbers are missing. The Journals names must be abbreviated and follow the Journal recommendations (ex. numbers in text). Several references may contain typographical errors, inconsistent capitalization, or discrepancies between in-text citations and the reference list. A thorough proofreading of the bibliography, including verification of journal titles, article titles, author names, and publication years, would improve accuracy and overall presentation quality.

Line 322- ex. Turner et al., 2000 – is not listed into References.

We scrutinized the references to ensure they are free of errors mentioned and also included DOI numbers to all that had them. We finally exchanged the in-text citations with numbers in the text.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents valuable research on the ecological services of invasive species, which represent one of the major threats to local biodiversity in ecosystems worldwide. Understanding the potential benefits of such species and exploring ways to manage and utilize them—particularly in situations where eradication is difficult or impractical—is an important and timely scientific objective. The study entitled “Invasive Phragmites australis may protect Long Island Sound salt marshes from sea level rise–driven coastal erosion” addresses a relevant ecological question with direct implications for conservation and coastal management.

Several issues need to be addressed before the manuscript can be accepted:

Several scientific names, at both the genus and species levels, are not italicized throughout the text. Please carefully revise the manuscript to ensure that all scientific names are consistently italicized according to standard nomenclatural conventions.

The in-text citations do not follow the journal’s required numbered format. According to the journal guidelines, reference numbers should appear in square brackets and be placed before punctuation (e.g., [1], [1–3], [1,3]). For citations with pagination, both brackets and parentheses should be used (e.g., [5] (p. 10) or [6] (pp. 101–105)). Please revise all in-text citations to comply with this format.

According to Plants of the World Online (POWO), GBIF, and World Flora Online (WFO), Spartina alterniflora Loisel. is now treated as a synonym of Sporobolus alterniflorus (Loisel.) P.M. Peterson & Saarela. Please update the species name accordingly and ensure consistent usage throughout the manuscript.

Please add the species author name to all scientific names at their first mention in the text.

In line 25, please avoid using the abbreviation “TOC” in the Abstract and spell it out in full.

It would be beneficial to include a photograph of Phragmites australis and its stands in their natural habitat in the Introduction, as this would provide valuable visual context and enhance the presentation of the species.

In line 78, according to Plants of the World Online, Spartina patens (Aiton) Muhl. is now treated as a synonym of Sporobolus pumilus (Roth) P.M. Peterson & Saarela. Please update the species name accordingly and ensure consistent usage throughout the manuscript.

In Figure 1 (Soil sampling locations), it would be helpful to include a zoomed-out map of the USA with the study area clearly highlighted. This would provide better geographic context and allow readers from outside the region to easily recognize the location of the sampling sites.

In lines 69–70, the sentence “dry ice to maintain a temperature of approximately 4 °C in the field upon return to the University of New Haven where they were immediately stored at −20 °C until processing” is repeated, as this information has already been stated earlier in Section 2.2 (Sample Collection). Please remove the duplication to improve clarity and avoid redundancy.

It is not advisable to begin the Conclusion with the phrase “In summary,” as the purpose of this section is to present the key outcomes of the research and explain how the findings advance scientific understanding. Please revise the opening of the Conclusion to focus directly on the main results and their scientific significance.

Author Response

Thank you for these constructive comments – our responses are provided below in bold

Several issues need to be addressed before the manuscript can be accepted:

We appreciate this observation. Scientific names were updated throughout the manuscript. We also made sure to italicize scientific names throughout the manuscript.

In-text citations were corrected to meet the journals standard.

We ensured that the species names were updated in text, tables and figures to reflect the updated names.

Please add the species author name to all scientific names at their first mention in the text.

Species author names were included at first mention.

In line 25, please avoid using the abbreviation “TOC” in the Abstract and spell it out in full.

Thank you for this observation, we spelled out the word total organic carbon in the abstract.

While this was initially thought to be a good idea, the images collected from the site did not do justice to the species and may require more than one photo to clearly show the physiognomy of each species studied.

This is very helpful and we worked to correct the names of the species throughout the manuscript.

A zoomed out map of the United States showing various states is now included in Figure 1.

The redundant statement was replaced with a statement that they were treated as the previous samples. Prior to processing.

Thank you for this observation, the words “In summary” were deleted and the conclusions re-worked to be more succinct.

Reviewer 3 Report

Comments and Suggestions for Authors

The study compares soil properties and carbon stocks between invasive Phragmites australis and native Spartina alterniflora in two Connecticut salt marshes. While the topic is relevant to coastal management under climate change, the manuscript suffers from inconsistencies in sampling design, unclear statistical reporting, and overinterpretation of results without adequate support. The writing is generally clear but occasionally lacks precision.

The sampling strategies between sites (Branford vs. Quinnipiac) differ markedly in timing, depth, and core diameter. This undermines direct comparison and limits the ability to draw generalized conclusions. The rationale for selecting 30 cm depth at Branford vs. 20-30 cm at Quinnipiac is not provided. Depth is critical for carbon stock calculations; inconsistency may bias results.
Non-parametric tests were used due to non-normal data, but the presentation of results (e.g., in Tables 1-2) reports means±SE, which is misleading for non-normally distributed data. Medians with interquartile ranges are more appropriate. The Scheirer-Ray Hare and Welch’s ANOVA results are reported without sufficient detail. Post-hoc comparisons are mentioned but not fully documented. The claim of “high heterogeneity” in P. australis is based on Levene’s test, but visual evidence is lacking.
The conclusion that carbon stocks are “comparable” between species is not fully supported by the data. At Branford, S. alterniflora had higher TOC in all zones (Fig. 5), yet the discussion downplays this difference.
The idea of “islands of resilience” is speculative and not directly tested. The link between bulk density and erosion resistance is assumed rather than measured.
No information is provided on soil core volume calculation or correction for compaction.
The acidification method for removing inorganic carbon is mentioned but not validated for marsh soils rich in carbonates.
Vegetation biomass data (Fig. 7) are presented without clear sampling protocols or statistical comparison.
The term “blue carbon” is used but not defined in the context of this study.

Author Response

Thank you for these constructive comments – our responses are provided below in bold

The sampling strategies between sites (Branford vs. Quinnipiac) differ markedly in timing, depth, and core diameter. This undermines direct comparison and limits the ability to draw generalized conclusions. The rationale for selecting 30 cm depth at Branford vs. 20-30 cm at Quinnipiac is not provided. Depth is critical for carbon stock calculations; inconsistency may bias results.

In our calculation of carbon (kgC/ha), depth was included (see equation 1). The reason for shallower samples at Quinnipiac Meadows was the dry/hard soils relative to the very moist soils at Branford. We added this explanation in the results section. Greater moisture may be the reason for increased carbon in the Sporobolus soils at Branford. Nonetheless, differences in soil depth may have introduced some experimental error to the results and this is acknowledged in the conclusion.

It must be noted that prior studies indicate a negative correlation between carbon content and depth (e.g., Bai et al. 2016) therefore most carbon should be in the upper 20cm or so. If this was the case in our samples, then the coalesced deeper samples could in fact underestimate soil carbon relative to the shallower ones.

Non-parametric tests were used due to non-normal data, but the presentation of results (e.g., in Tables 1-2) reports means±SE, which is misleading for non-normally distributed data. Medians with interquartile ranges are more appropriate. The Scheirer-Ray Hare and Welch’s ANOVA results are reported without sufficient detail. Post-hoc comparisons are mentioned but not fully documented. The claim of “high heterogeneity” in P. australis is based on Levene’s test, but visual evidence is lacking.

We agree that means and SE are not optimal for non-normally distributed data, however we included boxplots to further illustrate differences. We also included the test metrics for each test.

The conclusion that carbon stocks are “comparable” between species is not fully supported by the data. At Branford, S. alterniflora had higher TOC in all zones (Fig. 5), yet the discussion downplays this difference.

To address this issue, we removed the graph and statements comparing the two sites as this was not the objective of the study. To ensure the focus is on soil characteristics and that the two sites were used to expand the inferential scope, we restructured the graphs and to focus on the spatio-temporal aspects of the study.

The idea of “islands of resilience” is speculative and not directly tested. The link between bulk density and erosion resistance is assumed rather than measured.

We included literature to support this. A prior study found that increased bulk density resisted shearing and therefore erosive forces (Cahoon et al. 2021)

No information is provided on soil core volume calculation or correction for compaction.

Thank you for this observation. We measured soil core volume as a function of depth and surface area – we will include this in the methods. Compaction was avoided by avoiding forcefully pushing the corer into the soil during sampling. We also avoided walking on the site prior to sampling.

The acidification method for removing inorganic carbon is mentioned but not validated for marsh soils rich in carbonates.

According to both laboratories we worked with in analyzing the samples (Yale and UC Merced), acidification is a standard method for organic carbon in soils and is done to avoid including inorganic carbonates.

Vegetation biomass data (Fig. 7) are presented without clear sampling protocols or statistical comparison.

Since vegetation seemed to distract from the core study objective we removed references to vegetation sampling as it did not really add to the overall results – especially since vegetation was not collected from Quinnipiac Meadows.

The term “blue carbon” is used but not defined in the context of this study.

We included a definition of blue carbon in the introduction

Reviewer 4 Report

Comments and Suggestions for Authors

This manuscript presents a timely and nuanced investigation into the complex role of invasive Phragmites australis in salt marsh ecosystems, specifically contrasting its effects on soil carbon dynamics and physical structure against the native Spartina alterniflora. The study challenges prevailing assumptions by demonstrating that while P. australis promotes a denser soil matrix potentially enhancing physical resilience to erosion and sea-level rise, it does not consistently outperform the native species in carbon sequestration and introduces significant spatial heterogeneity in carbon stocks. The topic is of considerable importance for coastal management in the face of climate change. However, the manuscript requires substantial revision to meet standard academic formatting and clarity before publication. The writing exhibits numerous inconsistencies in formatting, citation, and presentation that detract from its scientific rigor and readability.
Major concerns center on structural, methodological, and interpretive issues.
(1) The title is misleadingly narrow, focusing only on erosion protection while the study equally addresses carbon storage; a title reflecting both key aspects would be more accurate.
(2) The introduction, while providing extensive background on biological invasion and Phragmites, offers limited synthesis of recent advances specifically linking invasion to the two ecosystem functions under investigation. More critically, it presents the "common assumption" that P. australis invasion increases carbon sequestration without citing key references that established or support this hypothesis (e.g., studies citing its larger biomass and slower decomposition). A concise explanation of the reasoning behind this widespread assumption is necessary to properly frame the study's investigative goal. Correspondingly, the discussion should then explicitly revisit and discuss why the present findings suggest this assumption may not hold universally, directly linking back to the introduced literature.
(3) Methodologically, two issues require clarification and justification. First, the use of different coring depths (30 cm vs. 20-30 cm) and corer diameters (5.5 cm vs. 2.5 cm) between the two study sites without explanation raises questions about the comparability of bulk density and carbon stock calculations. Second, while bulk density is a useful indicator, its adequacy as a sole proxy for erosion resistance should be discussed. Soil shear strength, organic matter quality, and root architecture are also critical determinants of stability. The manuscript should acknowledge that while higher bulk density likely contributes to resilience, it is part of a more complex mechanistic picture.
(4) In the results and figures, there are significant presentation flaws: the two maps in Figure 1 appear to have vastly different scale bars (there might be wrong one); individual sub-figures should be compiled into multi-panel figures with clear labels (e.g., Figure 7 is discussed before Figures 4-6); the sequence of figure citation in the text does not always match their appearance; and error bars are not explicitly defined. Furthermore, statistical notations such as "P" for p-values are not italicized.
(5) The discussion and conclusion sections would benefit from a more measured interpretation of the study's scope. As a detailed case study from two marshes in a specific region, the generalizability of the findings to other climatic, geological, and ecological settings, and their relevance to other invasive plant species, requires careful discussion. While the findings are valuable, explicitly outlining the conditions under which these trade-offs might be consistent or variable would strengthen the manuscript's impact and guide future comparative research. The conclusion section is currently verbose and could be powerfully condensed into a single, focused paragraph summarizing the key trade-offs and management implications without excessive repetition.
Minor concerns relate primarily to formatting and consistency.
(1) The keyword list is excessively long and includes abbreviations; it should be shortened to core terms spelled out fully.
(2) In-text formatting is inconsistent regarding paragraph indentation, has unnecessary blank lines, and uses an incorrect degree Celsius symbol (the degree Celsius symbol is incorrectly rendered as a superscript "o" followed by "C" instead of "°C").
(3) Typographical spacing is lacking around mathematical operators.
(4) Terminology is redundantly defined with full terms and acronyms repeated throughout.
(5) The italicization of species names is not consistently applied.
(6) Finally, the reference section is problematic: it uses numbered brackets instead of author-date citations, entries are not alphabetized, and several contain anomalous formatting. The references must be reformatted to match the journal's style guide, with an alphabetical list corresponding to author-year citations in the text.

Author Response

Thank you for these constructive comments – our responses are provided below in bold

(1) The title is misleadingly narrow, focusing only on erosion protection while the study equally addresses carbon storage; a title reflecting both key aspects would be more accurate.

We agree that the title was narrowly focused in an attempt to highlight the key takeaway. In this revision we include a more well rounded title to cover all aspects of the study. “Beyond Invasion: How Phragmites australis Modifies Soil Architecture, Nutrient Dynamics, and Carbon Sequestration in Long Island Sound Salt Marshes”

(2) The introduction, while providing extensive background on biological invasion and Phragmites, offers limited synthesis of recent advances specifically linking invasion to the two ecosystem functions under investigation. More critically, it presents the "common assumption" that P. australis invasion increases carbon sequestration without citing key references that established or support this hypothesis (e.g., studies citing its larger biomass and slower decomposition). A concise explanation of the reasoning behind this widespread assumption is necessary to properly frame the study's investigative goal. Correspondingly, the discussion should then explicitly revisit and discuss why the present findings suggest this assumption may not hold universally, directly linking back to the introduced literature.

We agree that that specific sentence when removed from the introduction lacks sufficient support. However, we have multiple statements and citations in the introduction that lend backing to the statement above. For instance we state the following

“Despite its reputation as a biological threat, invasive P. australis has been widely reported to provide superior ecosystem benefits relative to indigenous counterparts like S. alterniflorus and Sporobolus pumilus (Roth) P.M. Peterson & Saarela. (formerly Spartina patens (Aiton) Muhl), specifically regarding sediment stabilization and accretion [13, 14]. A study conducted at a St. Lawrence Estuary marsh found that invasive P. australis contributed more to soil volume and carbon stock than native Spartina spp. [15]. Similarly, [16] found that P. australis produced far greater above- and below-ground biomass than S. patens. Coupled with slower decomposition rates, it was hypothesized that this robust biomass production would lead to increased carbon sequestration and a physically denser peat layer. However, recent research suggests that anthropogenically driven changes, such as nutrient enrichment, may complicate this picture, potentially resulting in soil organic carbon (SOC) loss [17, 18, 19].”

The citations are:

Kiviat, E. (2013). Ecosystem services of Phragmites in North America. AoB Plants, 5, plt008. https://doi.org/10.1093/aobpla/plt008
Lathrop, R. G.; Windham, L.; Montesano, P. (2003). Does Phragmites expansion alter marsh landscapes? Estuaries, 26(2), 423–435. https://doi.org/10.1007/BF02696005
Gu, J.; van Ardenne, L. B.; Chmura, G. L. (2020). Invasive Phragmites increases blue carbon stock. J. Ge-ophys. Res. Biogeosci., 125(12), e2020JG005831. https://doi.org/10.1029/2020JG005831
Windham, L. (2001). Biomass production and decomposition in tidal marshes. Wetlands, 21(2), 179–188. https://doi.org/10.1672/0277-5212(2001)021[0179:COBPAD]2.0.CO;2
González‑Alcaraz, M. N.; et al. (2012). Storage of organic carbon in Phragmites australis stands. Geoderma, 185–186, 61–72. https://doi.org/10.1016/j.geoderma.2012.07.018
Mozdzer, T. J.; et al. (2023). Mining of deep nitrogen facilitates Phragmites australis invasion. Estuaries Coasts, 46, 998–1008. https://doi.org/10.1007/s12237-022-01120-0
Zhang, X.; et al. (2022). Nutrient enrichment decreases DOC sequestration. Ecol. Indic., 145, 109576. https://doi.org/10.1016/j.ecolind.2022.109576

(3) Methodologically, two issues require clarification and justification. First, the use of different coring depths (30 cm vs. 20-30 cm) and corer diameters (5.5 cm vs. 2.5 cm) between the two study sites without explanation raises questions about the comparability of bulk density and carbon stock calculations. Second, while bulk density is a useful indicator, its adequacy as a sole proxy for erosion resistance should be discussed. Soil shear strength, organic matter quality, and root architecture are also critical determinants of stability. The manuscript should acknowledge that while higher bulk density likely contributes to resilience, it is part of a more complex mechanistic picture.

We agree that the differences in core collection were not optimal and may have introduced some experimental error to the findings. This is acknowledged in the discussion and conclusions of the study to encourage further investigation. Nonetheless, we contend that the general trend (comparing species, not locations) is the focus of the study. Therefore, greater bulk density under one species versus the other should not be a function of collection method. As for the role of bulk density in shear strength, we agree with the reviewers suggestion to include the fact that a complex array of factors contribute to this and we included a statement in the discussion acknowledging it.

(4) In the results and figures, there are significant presentation flaws: the two maps in Figure 1 appear to have vastly different scale bars (there might be wrong one); individual sub-figures should be compiled into multi-panel figures with clear labels (e.g., Figure 7 is discussed before Figures 4-6); the sequence of figure citation in the text does not always match their appearance; and error bars are not explicitly defined. Furthermore, statistical notations such as "P" for p-values are not italicized.

Thank you for noting the scale bar error, we reviewed the maps in the original program and have now included the correct scales for both. We also re-worked the figures into individual images with multiple panels to improve their presentation. After re-doing the figures, the sequence of mentions changed in the revised manuscript

(5) The discussion and conclusion sections would benefit from a more measured interpretation of the study's scope. As a detailed case study from two marshes in a specific region, the generalizability of the findings to other climatic, geological, and ecological settings, and their relevance to other invasive plant species, requires careful discussion. While the findings are valuable, explicitly outlining the conditions under which these trade-offs might be consistent or variable would strengthen the manuscript's impact and guide future comparative research. The conclusion section is currently verbose and could be powerfully condensed into a single, focused paragraph summarizing the key trade-offs and management implications without excessive repetition.

Thank you for this constructive feedback – we worked to focus the discussion and conclusion to remove redundancies. The conclusion was also reduced to ensure the most critical message is delivered precisely.

Minor concerns relate primarily to formatting and consistency.
(1) The keyword list is excessively long and includes abbreviations; it should be shortened to core terms spelled out fully.

We removed the abbreviation and reduced the key word list to 8 terms.

(2) In-text formatting is inconsistent regarding paragraph indentation, has unnecessary blank lines, and uses an incorrect degree Celsius symbol (the degree Celsius symbol is incorrectly rendered as a superscript "o" followed by "C" instead of "°C").

Thank you for noting these errors, we corrected them throughout

(3) Typographical spacing is lacking around mathematical operators.

We inserted typographical spacing around the mathematical operators.

(4) Terminology is redundantly defined with full terms and acronyms repeated throughout.

To reduce redundancy we explained acronyms once (at first mention) and then used acronyms the rest of the manuscript. In some instances we refer to carbon bu TOC or just carbon.

(5) The italicization of species names is not consistently applied.

We double checked and ensured all species names are italicized.

(6) Finally, the reference section is problematic: it uses numbered brackets instead of author-date citations, entries are not alphabetized, and several contain anomalous formatting. The references must be reformatted to match the journal's style guide, with an alphabetical list corresponding to author-year citations in the text.

We reformatted the in-text citations to meet the journal standard, as chronological numbers in square brackets.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revisions have improved the quality of the paper, and in its current form, I consider the manuscript suitable for acceptance and publication.

Author Response

We wish to thank the Reviewer for their constructive edits that helped improve the manuscript.

Reviewer 4 Report

Comments and Suggestions for Authors

Thank you for your careful revisions in response to the previous feedback. The manuscript has been notably improved. I have a few minor yet important suggestions for your consideration:

Firstly, regarding the species nomenclature, I note the updated use of Sporobolus alterniflorus, which is taxonomically correct. However, given that the former name Spartina alterniflora remains deeply entrenched and is the identifier used in the vast majority of the historical and ecological literature on this invasive species, I strongly recommend explicitly including it in the abstract or keywords.

Secondly, there is an inconsistency in the formatting of species binomials upon their first introduction in the text; some include the authority (e.g., "Loisel.") while others do not. Please ensure that the full scientific name with authority is presented the first time each species is mentioned in the main text.

Thirdly, please format all statistical variables in italics throughout the manuscript, as is the standard convention. This includes symbols such as P and N.

Finally, to make the statistical comparisons in Figures 2 and 3 immediately clear to readers, please add explicit significance indicators (e.g., asterisks *, **, *** and 'ns' for non-significant comparisons) directly to the figures to denote group-wise differences, with a corresponding explanation in the figure legend.

Author Response

We appreciate your constructive feedback. Please see the responses below in bold.

We strongly agree with this and feel it's important that this manuscript be readily comparable to the large body of existing literature that uses the old name. To try and ensure that this is not overlooked, we included the old name in the simple summary, abstract. Key Words and Introduction. We hope that this reiteration will ensure other researchers can still relate to the findings. We included the old name in the summary, abstract and key words. However to ensure we maintain the Keyword limit, we deleted “invasive species”.

You are correct, we included the full names including authors at first mention for the following tat were missing

Phragmites australis (Cav.) Trin. ex Steud. subsp. australis
Phragmites australis (Cav.) Trin. ex Steud. subsp. americanus Saltonst., P.M. Peterson & Soreng

Thirdly, please format all statistical variables in italics throughout the manuscript, as is the standard convention. This includes symbols such as P and N.

We italicized all statistical symbols throughout the manuscript.

Finally, to make the statistical comparisons in Figures 2 and 3 immediately clear to readers, please add explicit significance indicators (e.g., asterisks *, **, *** and 'ns' for non-significant comparisons) directly to the figures to denote group-wise differences, with a corresponding explanation in the figure legend.

We added asterisks to each panel to signify the statistical significance of the comparison between species in each panel with an explanation.