the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Aug 2025
Vegetation-mediated surface soil organic carbon formation and potential carbon loss risks in Dongting Lake floodplain, China
Abstract. Sources and stabilization mechanisms of soil organic carbon (SOC) fundamentally govern the carbon sequestration potential of wetland ecosystems. Nevertheless, systematic investigations regarding SOC sources and molecular stability remain scarce in floodplain wetland environments. This study employed dual analytical approaches (stable isotope analysis and 13C nuclear magnetic resonance spectroscopy) to characterize surface SOC composition across three dominant vegetation communities (Miscanthus, Carex, and mudflat) in Dongting Lake floodplain wetlands. Key findings revealed: (1) Significantly elevated SOC concentrations in vegetated communities (Miscanthus: 13.76 g kg-1; Carex: 12.98 g kg-1) compared to unvegetated mudflat (6.88 g kg-1); (2) Distinct δ13C signatures across communities, with the highest isotopic values in Miscanthus (−22.67 ‰), intermediate in mudflat (−26.01 ‰), and most depleted values in Carex (−28.25 ‰); (3) Bayesian mixing models identified autochthonous plant biomass as the primary SOC source (Miscanthus: 53.3±10.6 %, Carex: 52.4 %±11.6 %, Mudflat: 47.5±12.5 %); (4) Spatial heterogeneity in POM contributions across sub-lakes, showing descending contributions from South (highest) > West > East (lowest) Dongting Lake; (5) Molecular characterization revealed O-alkyl C dominance (27.3–46.8 %), followed by alkyl C and aromatic C. Notably, Miscanthus soils exhibited enhanced O-alkyl C content (Alip/Arom) and reduced aromaticity/hydrophobicity indices, suggesting comparatively lower biochemical stability of its SOC pool. These results highlight the critical role of vegetation-mediated SOC formation processes and warn against potential carbon loss risks in Miscanthus-dominated floodplain ecosystems, providing a scientific basis for carbon management of wetland soils.
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RC1: 'Comment on egusphere-2025-2972', Anonymous Referee #1, 28 Aug 2025
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AC1: 'Reply on RC1', Zhengmiao Deng, 03 Sep 2025
General comments:
Sources and stabilization mechanisms of soil organic carbon (SOC) fundamentally govern the carbon sequestration potential of wetland ecosystems. The manuscript revealed that autochthonous plant as the primary SOC source in the Dongting Lake floodplain wetlands, while the contribution of allochthonous particulate organic matter exhibits spatial and vegetation-related variations. The study also reveals that a great risk of soil carbon loss potential in the Miscanthus community. In the context of global climate change and hydrological rhythms, it provides an important scientific reference for optimising the management of carbon sinks and improving soil carbon sequestration potential in floodplain wetlands. Overall, this topic is both interesting and scientifically valuable. I have some minor revise suggestions as below.
Response: Thank you for your positive feedbacks and valuable suggestions. We have adopted all your suggestions and responded to them one by one.Specific comments:
1. L25: Refine “surface SOC”.
Response: Thanks for the suggestions! L25 has been changed to: characterize surface SOC (0-20 cm) composition across three dominant vegetation communities.2.L29: Ensure the unit is consistent with that used in L28.
Response: Thanks for the suggestions! We have adjusted the unit to be consistent with the previous one.3. L33: Please write out the full name of “POM” upon first mention; the description of spatial heterogeneity in POM contributions is unclear.
Response: Thanks for the suggestions! We have stated the abbreviation (POM) at the location of the first particulate organic matter appearance; We have revised the description of spatial heterogeneity in POM contributions to “the spatial heterogeneity of the POM contribution to the surface SOC”.4.L37: Key values should be provided.
Response: Thank you very much for your detailed suggestion. L37 has been changed to: Miscanthus soils exhibited enhanced O-alkyl C content (44.75 %) (Alip/Arom:3.64) and reduced aromaticity (0.22) /hydrophobicity (0.68) indices.5.L57-66: Repeated organizational language with unclear expression; not supported by available literature.
Response: Thanks for the suggestions! L57-66 has been changed to: The sources of SOC vary significantly among different vegetation communities, depending on vegetation characteristics and hydrological conditions (Ni et al., 2025; Guo et al., 2025). For instance, in mangrove ecosystems, SOC is primarily derived from mangrove plant tissues, whereas in adjacent S. alterniflora marshes and tidal flats, it relies more heavily on fluvially imported particulate organic matter (POM) (Wang et al., 2024a). Vegetation influences SOC sources mainly through plant productivity and litter decomposition rates, while hydrological conditions regulate the input and deposition of allochthonous carbon (Guo et al., 2025; Xia et al., 2021). Moreover, even within the same type of vegetation community, SOC sources may exhibit spatial heterogeneity due to local topographic features and anthropogenic activities, leading to the accumulation of allochthonous carbon (Swinnen et al., 2020).6.L102: Change “SOC levels” to “SOC content”.
Response: Thanks for the suggestions! We have changed “SOC levels” to “SOC content”.7. L221: Provide the calculation formula for A/O-A.
Response: Thanks for the suggestions! We have provided the calculation formula for A/O-A, A/O-A= alkyl C/ O-alkyl C.8.L256-257: Please verify the data: “The annual sediment transport of the four tributaries was 484.1 × 10⁴ tons”.
Response: Thank you for remind us. We have verified that this data is correct.9.L267: Do the data in Table 1 represent mean ± standard deviation or standard error? Please clarify.
Response: Sorry we did not define the presentation format of the data. The expressed data represents mean ± standard error, which we have added in Table 1.10.What does the asterisk (*) in the figures represent?
Response: Sorry we did not specify what "*" represents. * indicates significant differences between different vegetation types at the P<0.05 level. We have already provided explanations in the caption.11.Discussion 4.1: suggested comparison of soil organic carbon content with other wetlands.
Response: Thanks for the suggestions! We added comparisons with soil organic carbon content of other wetlands, specifically “The surface SOC content of the Dongting floodplain wetland (11.12 g kg-1) was close to that of the Poyang Lake wetland (9.69 g kg-1) (Yuan et al, 2023) but lower than that of the forested wetland in the middle and lower Elbe River in Germany (33.73 g kg-1) (Heger et al, 2021).”12.L420-422: There is an error in the way this sentence is expressed. O-alkyl C constitutes the dominant fraction (27.3–46.8 %) of SOC in Dongting Lake wetlands Consistent with other research findings, rather than the cellulose and hemicellulose components of plant litter decompose rapidly to produce carbohydrates.
Response: We are sorry for the mistake. L420-422 has been changed to: Specifically, the cellulose and hemicellulose components of plant litter decompose rapidly to produce carbohydrates (Mckee et al., 2016). O-alkyl C has also been found to be the dominant fraction of SOC in other lakes or river wetlands (Yang et al., 2023; Wang et al., 2011).13.L449-456: The risk of loss of soil carbon pools in Miscanthus community is higher......, this is an important conclusion. I suggest you add some scientific advises to migrate this loss potential at the end of this paragraph.
Response: Thanks for the suggestions! We have added some scientific advises to migrate this loss potential at the end of this paragraph, specifically“Therefore, hydrological management strategies such as regulating water levels or extending flood duration could be applied to maintain anaerobic conditions in Miscanthus soil, thereby potentially reducing the decomposition rate and loss of SOC.”Citation: https://doi.org/10.5194/egusphere-2025-2972-AC1
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AC1: 'Reply on RC1', Zhengmiao Deng, 03 Sep 2025
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RC2: 'Comment on egusphere-2025-2972', Anonymous Referee #2, 14 Oct 2025
For a river-connected floodplain wetland with a total area of 2,564 km² in China, sources and structure of soil organic carbon (SOC) were analysed using stabile isotop techniques and the 13C NMR method. For analysis, soil samples from of soil depth 0-20 cm were taken for 31 plots of 1x1 m.
L89, "sources and stability": The authors infer stability from SOC structure, which they analysed using the 13C NMR method - is this unambiguously possible?
L98ff: The hypotheses should be briefly justified not just stated
L131: 31 sampling sites of 1x1 m for area of 2564 km² - please explain why these sites were representative of the entire floodplain.
L149: units of VOC are inconsistent with eq. 1
L161: sum ID is unclear if I_WD is already the number of days when WD>0
L221: four indicators are presented as equations without numbering. What are the units of the terms presented in those equations?
L238: Please explain more detail on the approach to quantify source contributions.
Citation: https://doi.org/10.5194/egusphere-2025-2972-RC2
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Sources and stabilization mechanisms of soil organic carbon (SOC) fundamentally govern the carbon sequestration potential of wetland ecosystems. The manuscript revealed that autochthonous plant as the primary SOC source in the Dongting Lake floodplain wetlands, while the contribution of allochthonous particulate organic matter exhibits spatial and vegetation-related variations. The study also reveals that a great risk of soil carbon loss potential in the Miscanthus community. In the context of global climate change and hydrological rhythms, it provides an important scientific reference for optimising the management of carbon sinks and improving soil carbon sequestration potential in floodplain wetlands. Overall, this topic is both interesting and scientifically valuable. I have some minor revise suggestions as below.