| 26 Feb 2026
Root turnover and soil indicators capture belowground recovery following saltmarsh restoration
Abstract. Coastal wetlands, including saltmarsh, are highly productive ecosystems, with carbon- and nutrient-rich soils supporting biodiversity. Beyond carbon stocks and sequestration, the responses to restoration of these nutrient-rich and structurally complex soils remain poorly defined for coastal wetlands, especially in saltmarsh ecosystems restored by exclusion fencing. This study used a space-for-time approach to evaluate belowground responses in Salicornia quinqueflora-dominated saltmarsh 25 years after ungulate exclusion in Swan Bay, Victoria, Australia. We monitored surficial soil physicochemical characteristics, root and standardised litter decomposition, and root molecular composition across Grazed, Restored, and Natural Reference sites. Restored and Reference sites had ≥20 % higher vegetation cover and 2–3-fold higher percent soil carbon and nitrogen content, with 2.5-fold lower shear vane soil strength compared to Grazed sites. However, carbon and nitrogen stocks in the top 10 cm were not significantly different across sites (means ranging 30–36 Mg C ha-1) due to elevated bulk density at Grazed sites caused by compaction from ungulates. Salicornia quinqueflora root litter decomposition was slowest in Natural Reference sites, with molecular composition showing preservation of recalcitrant lignin in the Reference and Restored sites, indicating greater soil carbon preservation capacity. In contrast, roots decomposing in Grazed sites showed increased nitrogen and phenolic compounds indicating greater microbial-driven turnover. This study demonstrates that exclusion fencing can restore saltmarsh soil function and promote long-term resilience, particularly through improved preservation of recalcitrant organic matter material decades after intervention. By highlighting shifts in surface soil structure and organic matter preservation, this study shows why soil quality metrics beyond carbon stocks are essential for accurately evaluating restoration outcomes.
General comments
The study by Olsson et al. uses a space-for-time approach to evaluate the impact of restoration, through ungulate exclusion, on soil properties and carbon sequestration in saltmarsh ecosystems. The authors show that soils in areas subjected to exclusion fencing resemble natural reference conditions after 25 years, suggesting that this is an effective measure for improving physical, chemical, and biological soil properties. While studies assessing restoration outcomes in saltmarsh ecosystems often focus on only a limited number of indicators of belowground ecological function, this study examines a wide range of soil quality metrics. In particular, the authors highlight soil strength as a potentially useful indicator of belowground recovery. Restored and natural reference sites exhibited greater preservation of surficial recalcitrant carbon stocks, whereas enhanced microbial turnover likely occurred in disturbed soils in grazed saltmarshes. Overall, the study demonstrates the potential of exclusion fencing as a restoration strategy to enhance organic carbon stabilization in saltmarsh ecosystems.
The manuscript is clearly written and will likely be of interest to researchers and stakeholders working on saltmarsh restoration, as well as to a broader audience concerned with blue carbon sequestration.
Specific comments
1. The authors could better justify why only the top 10 cm of the soil profile was sampled and analyzed, given that greater depths are typically included in standard blue carbon stock assessments, as noted in the manuscript. Expanding the discussion on how well surface soil patterns reflect deeper soil conditions and total carbon stocks would strengthen the interpretation of the results and provide useful context for readers.
2. There is a general lack of consistency between figure/table references and the corresponding content. Please ensure that all references correctly match the figures and tables cited.
Examples of mismatches include:
3. The authors state that ungulate exclusion through fencing is an attractive restoration approach due to its low cost and minimal intervention, and that large-scale wetland restoration is increasingly needed. However, these landscapes are also used for livestock grazing. The authors could potentially strengthen the discussion by briefly addressing under which conditions exclusion fencing is most appropriate or efficient.
Technical corrections
Line 53 – 54: The sentence starting with “There is an increasing…” appears out of context and disrupts the flow. Consider rephrasing. Also, motivate why there is an increasing demand for larges-cale wetland restoration.
Line 487: Remove “the” after “preservation”.
Line 526 – 529: This sentence is difficult to follow and should be simplified for clarity.
Line 525: Please clarify the mechanism by which low nutrient availability would stimulate root turnover.
Figure 7: Variable names overlap in the figure, which reduces readability.
Figure 8: It is not clearly visible in the figure that root decomposition is lower in the restored and natural reference sites. This could potentially be made clearer. Additionally, the figure appears to suggest higher aboveground biodiversity in the natural reference site, which differs from the description in the text.
Supplementary Materials: The title does not match with the title of the manuscript and should be corrected.