Coastal agriculture has been adopted to increase agricultural productivity, whereas its effects on blue carbon ecosystem function and greenhouse gas (GHG) exchange dynamics are unclear. This research examined the impact of tidal saltwater irrigation on agronomic traits, CO2 uptake, and CH4 and N2O emissions within a coastal rice ecosystem (tidal-influenced and saline), and explored the microbial mechanisms responsible for GHGs mitigation. The study was conducted over 2 years on Chongming island, Shanghai, China. Here, the use of 6 parts per thousand saltwater for irrigation in sea rice cultivation led to an increase in net ecosystem CO2 exchange and gross primary productivity, mitigated CH4 and N2O emissions through tidal saltwater treatment with a projected decrease in CH4 emissions during the tillering stage, and was accompanied by a marked upregulation of the AcsB gene associated with CO2 fixation as well as the PmoA and Nirk2 genes involved in CH4 and N2O oxidation. Despite a decrease in plant height, this approach promoted tillering, thereby increasing shoot dry mass and ultimately maintaining rice yields without reduction. The study further revealed the combined CO2-equivalent emissions of CO2, CH4, and N2O during the tidal saltwater irrigation period, with reductions ranging from 22 % to 39 % for two different sea rice varieties. Therefore, the experimental simulation of tidal saltwater in a coastal rice system demonstrated its ability to sustain yield, increase carbon uptake and mitigate GHG emissions, although the effects were not statistically significant. We suggest that coastal rice cultivation using natural tidal irrigation is an effective approach to strengthen the ecological of coastal tidal mudflats by reducing GHG emissions and enhancing rice yields.

Salt marshes play a critical role in buffering the impacts of extreme events, stabilizing coastlines, and regulating sediment transport. Along the eastern coast of China, various restoration and management strategies have been widely implemented under the national Special Action Plan for the Comprehensive Control of Spartina alterniflora. However, the effectiveness of these management strategies under extreme climate events remains unclear. This study evaluated the hydrodynamic-sedimentary-morphological responses of four sites representing three post-eradication management types (engineering-based restoration with breakwaters, native vegetation restoration, and untreated bare flats) during typhoon events. During the typhoon events, the breakwater protected site experienced the strongest hydrodynamic forcing, with peak significant wave height exceeding 0.5 m and wave energy >200 J m(-2), whereas vegetation restoration sites generally maintained lower energy conditions, with wave height remaining below 0.3 m. The untreated bare flat showed the most intense sediment disturbance, with turbidity peaks >2000 FTU, compared with <1000 FTU at vegetation restoration sites, and bottom shear stress peaks >1.0 N m(-2) at engineering and bare flat sites. Morphological analyses indicated that the engineering restoration site showed the strongest resistance to erosion, with elevation changes constrained within +/- 0.1 m, whereas the untreated bare flat experienced severe erosion, with local elevation loss peaks >0.5 m. Vegetation restoration sites exhibited intermediate geomorphological stability and post-storm sediment retention within vegetated areas (0.1 - 0.2 m deposition). Overall, these results demonstrate divergent hydrodynamic-sedimentary-morphological responses among management strategies under extreme disturbances, highlighting the importance of integrated ecological and engineering design for coastal wetland management and climate adaptation following large scale S. alterniflora eradication.

Background and Aims Mangrove ecosystems serve as critical blue carbon sinks, yet the microbial mechanisms governing iron-bound organic carbon (Fe-OC) formation under varying salinity conditions remain poorly understood. This study aims to elucidate the microbial-mediated pathways controlling Fe-OC formation in Aegiceras corniculatum rhizosphere soils across a natural salinity gradient (1.5–2.4‰). Methods We employed an integrated biogeochemical and shotgun metagenomic approach to analyze rhizosphere and bulk soils from the Nanliu River Estuary, China. Structural equation modeling (SEM) was utilized to identify the dominant mechanistic pathways linking environmental factors, microbial metabolism, and Fe-OC formation. Results Under increasing salt stress, absolute Fe-OC content declined from 15.2 to 4.0 mg·g⁻¹, yet its proportion within total organic carbon increased from 34.2% to 61.8%. Metagenomic analysis revealed stable functional gene diversity despite significant taxonomic turnover, demonstrating inherent functional redundancy. Iron oxidation genes were enriched in saline flats, while carbon fixation genes concentrated in fresher sites. SEM identified salinity as the master environmental control (R² = 0.67), operating primarily through a dominant pathway: salinity → iron oxidation genes → iron oxides → Fe-OC. Conclusion Mangrove root metabolism and microbial functional genes synergistically mediate soil iron-carbon binding. Salinity acts as the primary environmental control through both direct geochemical effects and indirect pathways via microbial community restructuring, highlighting the importance of functional redundancy in maintaining ecosystem resilience under environmental stress.

Newly established salt marsh vegetation may exert unexpected effects on sediment dynamics, yet direct high-resolution evidence remains scarce. To address this gap, this study monitored early-stage colonization of Scirpus mariqueter at Chongming Dongtan using Unmanned Aerial Vehicle (UAV) imagery acquired from July to September 2021. Across all monitoring periods, a dynamic thresholding approach using the Green Leaf Index (GLI) enabled high-accuracy classification of vegetated versus unvegetated mudflats, with overall accuracies exceeding 99

Mangrove soils are vital blue carbon reservoirs; however, the mechanisms governing organic carbon stabilization and vertical distribution dynamics during restoration remain poorly constrained. We systematically sampled soil profiles (0-100 cm) from Kandelia obovata plantations aged 5, 10, 15, and 20 years to analyze spatiotemporal dynamics of organic carbon fractions, iron-bound organic carbon (Fe-OC), iron oxides, and microbial communities. Results revealed that all carbon fractions followed a unimodal accumulation pattern, peaking at the 15th year before declining, challenging the traditional linear accumulation paradigm. The vertical distribution of Fe-OC exhibited a fundamental shift, with the center of Fe-OC enrichment shifting progressively from surface soils (0-20 cm) in early-stage stands to deep soil layers (80-100 cm) in mature stands, reflecting a reorganization of iron-mediated carbon stabilization along the soil profile. In 20-year stands, a notable increase in the Fe3+/Fe2+ ratio signified a critical redox transition, mechanistically linked to enhanced nitrification and reduced methanogenesis. Variance partitioning analysis demonstrated that soil depth accounted for 18.78% of the variation in carbon fractions-nearly four times the 4.85% attributable to stand age-underscoring the critical importance of deep soil carbon. Structural equation modeling identified a negative correlation between SOC and the Mineral Associated Organic Carbon (MAOC)/SOC ratio (β = -0.282), suggesting progressive constraints on mineral protection capacity. We identify an apparent intermediate-stage peak (10-15 years) in carbon accumulation and stabilization within the studied chronosequence, providing a scientific basis for evaluating carbon storage and stabilization potential and optimizing management strategies for restored mangrove ecosystems.

Invasive species eradication, while necessary for biodiversity conservation, frequently triggers loss of ecosystem functions previously provided by the invader, creating management dilemmas for large-scale restoration. China's Spartina alterniflora removal program (68,000 ha, 2023-2025) exemplifies this challenge: despite degrading biodiversity, the S. alterniflora delivers substantial coastal protection and carbon sequestration services. Strategic post-eradication restoration requires explicit evaluation of which ecosystem functions to prioritize at which locations. We developed a spatially explicit framework integrating species distribution modeling with scenariobased optimization to identify optimal native vegetation allocation strategies for ecosystem function recovery following S. alterniflora eradication in the Yangtze Estuary. We modeled habitat suitability for functionally distinct native species (Phragmites australis and Scirpus mariqueter) and designed four restoration scenarios: Environmental Suitability (ES, baseline) and three optimization scenarios targeting Carbon Stock (CS), Coastal Protection (CP), and Biodiversity Protection (BP). Optimization scenarios achieved target ecosystem function improvements (CS: +15 % carbon stock; CP: +71 % wave attenuation; BP: +15 % biodiversity indices), incurred 7-14 % reductions in non-target functions. Carbon storage and coastal protection exhibited synergies through shared biomass dependence: the CS scenario achieved +43 % wave attenuation despite prioritizing carbon, while the CP scenario co-delivered +7 % carbon stock gains. In contrast, biodiversity enhancement through habitat heterogeneity traded off both biomass-dependent functions: the BP scenario reduced carbon stock by 7 % and wave attenuation by 14 % relative to the ES baseline. Given these trade-offs, we recommend spatially differentiated implementation: CP along erosion-prone shorelines, CS in rapidly accreting zones, and BP in areas adjacent to protected habitats. This framework provides a transferable approach for balancing multiple ecosystem functions in S. alterniflora post-eradication coastal restoration worldwide.

Delta regions worldwide face escalating coastal flood risks driven by the compound effects of sealevel rise (SLR) and vertical land motion (VLM). Existing studies often analyze these hazards separately and rely heavily on simplified static inundation models, limiting the accuracy of flood impact assessments and neglecting dynamic socioeconomic factors. This study develops an integrated framework combining high-resolution VLM monitoring (SBAS-InSAR), dynamic hydrodynamic modeling (LISFLOOD-FP), and socioeconomic projections (Shared Socioeconomic Pathways: SSP1-2.6, SSP2-4.5, SSP5-8.5) for comprehensive flood impact evaluation in three globally significant deltas: the Ganges-Brahmaputra-Meghna (GBM), Mississippi, and Yangtze. Results highlight severe and spatially variable subsidence rates-most notably in the GBM Delta (-8.98 mm/year), followed by the Mississippi (-2.93 mm/year) and Yangtze (-1.60 mm/year)- with human activities likely playing an important role in driving surface deformation. Projected flood scenarios (2050 and 2080) indicate significant increases in inundation extents and exposed populations and economic assets, particularly under combined SLR + VLM scenarios. The Yangtze Delta shows the highest economic exposure (up to approximately 1 trillion USD), whereas the GBM Delta exhibits the greatest demographic vulnerability, potentially affecting approximately 20 million individuals. The relative contributions analysis emphasizes an increasing dominance of SLR over time, especially under high-emission scenarios. These findings underscore the critical importance of tailored, region-specific adaptation strategies including resilient infrastructure, nature-based solutions, and adaptive spatial planning.

Salt marshes provide critical coastal protection by attenuating waves, yet their performance under extreme storm conditions and subsequent recovery have lacked quantitative assessment. This study quantifies temporal variations in wave attenuation capacity across a complete storm cycle (before-during-after) at a Scirpus mariqueter marsh in the Yangtze Estuary, and evaluates cumulative impacts under storm sequences through numerical modeling. Our results show: (1) Storm landfall led to significant reduction in wave attenuation capacity of salt marshes, with wave damping coefficient (beta) decreasing substantially in the post-storm period; (2) The weakened wave attenuation capacity of salt marshes was attributed to storm-induced vegetation damage in stem density, with recovery taking more than a few weeks; (3) Under the scenario of storm sequences, cumulative damage in stem density caused significant decline in wave attenuation capacity of salt marshes, with beta gradually decreasing until the vegetation disappeared completely. This study reveals the vulnerability of salt marsh wave attenuation to storm disturbances, particularly under storm sequences, providing critical insights for coastal wetland management under increasing storm frequency.

Mangrove ecosystems serve as important blue carbon sinks, yet the microbial mechanisms governing iron-bound organic carbon (Fe-OC) formation under varying salinity conditions remain poorly understood. This study aims to elucidate the microbial-mediated pathways controlling Fe-OC formation in Aegiceras corniculatum rhizosphere soils across a natural salinity gradient (1.3‰–2.4 ‰). We employed an integrated biogeochemical and shotgun metagenomic approach to analyze rhizosphere and bulk soils from the Nanliu River Estuary, China. Structural equation modeling (SEM) was utilized to identify the dominant mechanistic pathways linking environmental factors, microbial metabolism, and Fe-OC formation. Under increasing salt stress, absolute Fe-OC content declined from 15.2 to 4.0 mg·g⁻1, yet its proportion within total organic carbon increased from 33.5

Algal-bacterial interactions regulate the production and fate of marine particulate organic carbon (POC), yet their capacity to generate long-lived carbon sinks remains unclear. Using a two-year, nutrient-self-sustaining co-culture of Synechococcus and its mutualistic microbiota, we demonstrate that sustained algal-bacterial interactions promote the progressive accumulation of recalcitrant POC. Continuous release of algal-derived organic substrates, coupled with repeated microbial enzymatic reworking, produced inert organic particles, with ~26% resisting remineralization and forming a stable recalcitrant particulate carbon pool. Radiocarbon (Δ14C) analyses revealed an apparent age offset exceeding 400 years for POC formed within only two-year experiment. This “aged” signature likely results from algal assimilation of fossil-fuel-14C-depleted atmospheric CO2 followed by accumulation in generated recalcitrant POC. By demonstrating that apparent radiocarbon age can become decoupled from actual residence time, these results provide insights into the interpretation of “old” marine POC and highlight the important roles of algal-bacterial interactions in ocean particulate carbon sequestration. Sustained algae-bacteria interactions generate recalcitrant particulate organic carbon with aged radiocarbon signatures within years, revealing an overlooked ocean carbon storage pathway and complicating interpretations of old marine carbon pools.

Macroalgae are dominant primary producers that drive carbon sequestration in coastal ecosystems. Macroalgal carbon sequestration primarily refers to the long-term storage of macroalgae-derived organic carbon in the ocean. However, calcium carbonate (CaCO3) formation is frequently observed in non-calcifying macroalgal environments, suggesting the existence of an overlooked inorganic carbon process in macroalgal ecosystems. Here, we introduce multiple pathways that may drive CaCO3 formation in macroalgal ecosystems. These include the effects of macroalgal photosynthesis and carbon-concentrating mechanisms on the seawater carbonate system, the role of phycosphere interfacial properties in facilitating CaCO3 nucleation, and the macroalgae-bacteria synergy that promotes CaCO3 formation. We identified several current knowledge gaps—the unclear carbon sequestration or source effect of CaCO3 formation in macroalgal ecosystems and the stability of CaCO3 minerals in macroalgal ecosystems—that require further investigation. This review advances the understanding of macroalgal carbon cycling beyond organic pathways and emphasizes the importance of a comprehensive assessment of macroalgal carbon sequestration, including that of inorganic carbon.

Tidal wetlands are critical natural assets, yet they face dual pressures from anthropogenic development and climate change. While tidal wetland loss is well-documented, habitat fragmentation - and its consequences for ecological connectivity - remains poorly quantified at large scales. This study investigates changes in tidal wetland area and structural connectivity, the latter assessed through the foreground area density metric, along the mainland coast of China from 2000 to 2022. Using high-resolution global annual 30-m wetland maps, we quantified pixel-level tidal wetland gain, loss, and fragmentation and integrated these metrics to identify landscape-scale patterns. Our results show a net tidal wetland loss of 5.0% (approximately 646 km2), with a simultaneous decline in mean national connectivity from 77.4% to 72.2% over the same period. Landscape clustering analysis revealed six distinct patterns of change. This analysis showed that approximately 14% of coastal units experienced severe ecological degradation characterized by both substantial net area loss and a significant increase in fragmentation. We found that transitions between tidal wetlands and open water (i.e., erosion and accretion) had a stronger effect on the connectivity of persistent tidal wetland patches than direct anthropogenic land-cover conversions. These findings suggest that China's transition from exploitation-driven to protection-oriented policy could (i) integrate ecological connectivity into wetland monitoring frameworks, (ii) explicitly manage seaward erosion and sediment processes in addition to regulating reclamation, and (iii) prioritize restoration that reconnects existing wetlands as well as expanding total area, to enhance long-term coastal resilience.

With increasing frequency and intensity under global climate change, storms, particularly typhoons, have become critical drivers reshaping coastal morphology. However, researches capturing the full morphodynamic sequence, especially the pre-landfall phase, remain scarce due to the challenges of field observations under extreme conditions. To address this, continuous observations were conducted throughout the Typhoon Fung-wong on the Yangtze Estuary intertidal flat. Here we found that, the loose and easily erodible surface layer of the intertidal mudflat was primarily eroded prior to typhoon landfall, exposing stiff, well-consolidated subsurface sediments. Subsequently, bed-level change remained minimal during peak hydrodynamics at typhoon landfall, showing that vertical sediment properties modulate morphodynamic responses. The decade-long continuous observations at the Sheshan Station in the Yangtze Estuary confirmed this severe pre-landfall erosion which also appears common across both China and the United States. This highlights the importance of pre-landfall erosion and sediment stratification in storm-driven coastal change prediction and management.

Coastal saltmarshes are increasingly recognized for their role in mitigating agricultural pollution, yet their function in regulating pesticide transport via groundwater-surface water interactions remains poorly understood. Here, we quantify pesticide fluxes across the groundwater-surface water interface in a Yellow Sea saltmarsh using 222Rn as a tracer of submarine groundwater discharge (SGD) and analyze 20 commonly used pesticides in porewater and surface water. We find that 80% of pesticides are retained within the saltmarsh, with a mean removal rate of 170±41 μg m-2 day-1. Only a few hydrophobic compounds (e.g., tricyclazole) are exported to coastal waters via SGD. Extrapolation to China's total saltmarsh area suggests an annual removal of ∼185 tons, equivalent to 29% of riverine pesticide inputs. Historical wetland loss has reduced this natural filtration capacity, but restoration could enhance removal by 78%. Our results demonstrate that saltmarshes act as net sinks for most pesticides, challenging the paradigm of SGD as a contaminant source. These ecosystems provide a critical nature-based solution for coastal pesticide pollution control, emphasizing the need to integrate wetland conservation into watershed management policies.

Coastal wetlands face dual threats from climate change and human disturbances, while they provide important ecosystem functions and deliver essential ecosystem services. Exploring the drivers behind coastal wetland changes will benefit sustainable coastal ecosystem management. Based on GlobaLand30 data, this study systematically assessed the spatiotemporal changes and drivers of China’s coastal marsh changes during 2000–2020 by incorporating land-use transformation process and various anthropogenic and environmental factors from public datasets. Our findings revealed a net increase of 865.8 km2 in coastal marsh area during 2000–2020, with distinct regional variations. Coastal marsh changes were more evident north of 30°N, particularly in the Bohai Rim region (37–41°N) and the Yangtze River Delta (30–33°N). Over 75% of major coastal marsh gains (> 1,250 ha) and losses (> 1,000 ha) based on 25 km2 hexagonal grids occurred in these two regions during 2000–2020. The increase in the proportion of major coastal marsh loss grids (> 1,000 km2) from 80.0% to 89.8% in these two regions during 2010–2020 suggests that some areas continued to deteriorate, highlighting that total area changes may mask important local dynamics. While driving factors varied across latitudes, land reclamation remained the dominant reason for coastal wetland loss. Reclamation induced coastal marsh loss accounting for over 60% of the total losses across all sea regions during different periods. In the Bohai Rim, the latitudinal distribution of marsh losses aligned with aquaculture changes patterns, while marsh gains primarily resulted from ecological recovery. In the East China Sea region where the Yangtze Delta is located, accretion contributed over 65% of total gains during both 2000–2010 and 2010–2020 periods. The areas of significant coastal marsh changes in the East China Sea region spatially overlapped with the distribution range of Spartina alterniflora. Based on the analysis of driving forces and ecological issues, this study proposed region-specific adaptive management strategies. Future research should strengthen the quantitative analysis of multiple driving forces’ interactions to provide a scientific basis for developing more targeted land-sea management strategies.

The global invasive species, Spartina alterniflora has caused significant damage to coastal wetland ecosystems in China. This study evaluated the effectiveness and ecological impacts of two S. alterniflora management strategies in the Yangtze River estuary: Haloxyfop-R-methyl application and repeated mowing (once at the early flowering stage and once nine weeks later). The effectiveness of S. alterniflora control, and macrobenthos and bacterial community responses were compared at the Haloxyfop-R-methyl site, repeated mowing site, a control site, and a mud site during 2022-2023, and sediment physicochemical properties were also assessed. One year after Haloxyfop-R-methyl application, the density, aboveground biomass, height, and regenerated S. alterniflora were significantly reduced by 84 %, 94 %, 80 %, and 99 %, respectively. Mowing reduced the density, aboveground biomass, and height by 28 %, 78 %, and 29 %, respectively. At the Haloxyfop-R-methyl site, the biomass and Chao1 index of macrobenthos were significantly decreased compared with the control. There were significant differences in the macrobenthos community structure between the Haloxyfop-R-methyl and mowing sites compared to the control. Haloxyfop-R-methyl application and mowing did not significantly alter the α-diversity of bacterial communities but had an impact on the bacterial community structure, with the main indicator species differing among sites. Vegetation changes, sediment moisture content, total organic carbon content, and ammonium nitrogen concentration were the main factors influencing the composition of macrobenthos and bacterial communities at all sites. In summary, the Haloxyfop-R-methyl strategy better controlled S. alterniflora in coastal wetlands, while the repeated mowing strategy resulted in less disturbance of the major biological groups.

River deltas are critical socio-economic and ecological regions but face heightened flood risks due to climate change and urbanization. Taking the Ganges-Brahmaputra-Meghna (GBM) River Delta, the Mississippi River Delta, and the Yangtze River Delta as case studies, this research aims to reveal the characteristics and formation mechanisms of human adaptation to flood risks across different deltaic regions. Through integrating hydrodynamic modeling, spatiotemporal analysis, and multi-source datasets, this study systematically investigates flood adaptation characteristics across three major deltas based on a newly developed comprehensive framework of Human-Flood Distance (HFD) and resilience. The results show that: spatially, while these three deltas exhibit varying degrees of inundation extent, each faces unique flood vulnerability challenges; temporally, the GBM River Delta exhibits stabilized population growth and HFD recovery after initial contraction, the Mississippi River Delta shows significant fluctuations in both population and HFD, while the Yangtze River Delta demonstrates continuous population growth with steady HFD increase; in terms of adaptation mechanisms, resilience assessment indicates that the Mississippi River Delta demonstrates the highest resilience, primarily driven by recovery capacity, the Yangtze River Delta shows limited but structurally supported resilience, while the GBM River Delta exhibits negative indices due to multiple constraints. These findings emphasize the importance of developing context-specific flood risk management strategies and provide feasible flood prevention solutions for policymakers, particularly in formulating adaptation strategies that comprehensively consider both flood safety and sustainable development.

China has initiated nationwide management projects targeting the invasive plant Spartina alterniflora in coastal zones. while the impact of different S. alterniflora eradication strategies on carbon fluxes remains unclear. This study investigated the effects of different strategies (application of Haloxyfop-R-methyl (HPEM) and repeated mowing (Mowing)) on the efficiency in eradicating S. alterniflora and the difference in carbon fluxes (CO2、CH4) through field experiments, futher analyzing the relationship between sediment physicochemical properties, and microbial communities and their relationship with carbon fluxes over a one-year period. Compared to Mowing, HPEM is more effective in eradicating S. alterniflora. Moreover, HPEM initially acted as a CO2 source before the growing season, while repeated mowing sites consistently functioned as CO2 sinks. Methane emissions at the HPEM site were significantly higher than those at Mowing and S. alterniflora sites during the non-growing season. Temperature and plant biomass were the main factors influencing carbon fluxes. Furthermore, we found that different eradication strategies significantly altered the soil microbial community structure, and these changes in microbial communities further influenced ecosystem respiration (ER), but had no significant impact on CH4 emissions. Therefore, we assumed that the elevated CH₄ emissions at the HPEM site are primarily driven by the decomposition of dead plant material. Overall, we recommend repeated mowing as an effective long-term management strategy for controlling S. alterniflora. In areas requiring rapid and thorough removal of S. alterniflora, Haloxyfop-R-methyl can be employed, but vegetation should be promptly cut down after treatment to minimize the negative environmental impact of methane emissions.

Coastlines are increasingly threatened by natural hazards such as intensifying storms, flooding, and erosion. The safety of lives and property in coastal zones can only be ensured when the biophysical capacity for coastal protection services adequately meets demand. Yet existing capacity-demand models often fail to account for the combined impacts of marine and terrestrial hazards (e.g. extreme rainfall coinciding with storm surges) and the mitigating effects of human critical infrastructure (e.g. dikes). To address this gap, we analyzed 228 county-level coastal assessment units along the Chinese mainland. First, we measured the biophysical capacity of coastal protection services using five indicators related to natural ecosystem properties. Next, we evaluated demand for coastal protection services by integrating six natural hazard indicators, four human exposure indicators, and four social adaptive capacity indicators into a risk reduction model. Finally, we identified nine distinct types of capacity-demand relationships across space (High-Low, High-Medium, High-High, Medium-Low, Medium-Medium, Medium-High, Low-Low, Low-Medium, and Low-High). Seventy-seven counties exhibited relatively low capacity and relatively high demand, located mostly in Guangdong and Jiangsu provinces. Furthermore, we found that many economically underdeveloped counties showed capacity-demand mismatches (e.g. the coastal counties of Hainan Province), perhaps because local infrastructure development has not kept pace with overall economic growth. This study provides a comprehensive framework for identifying spatial patterns of coastal protection services capacity-demand mismatches, thereby informing decision-making to enhance disaster resilience in China's coastal zones.

The salt marsh ecosystem is vulnerable to disturbances like vegetation invasion, which alter community structure and ecosystem functions, particularly blue carbon sequestration. While previous studies have mainly focused on localized carbon storage post-Spartina invasion, there is a lack of comprehensive seasonal dynamics and multi-regional comparative analyses of carbon fluxes. This study evaluated the impacts of Spartina species invasion on carbon fluxes in salt marsh wetlands across China and Denmark. Both regions, sharing the same native plant species, Phragmites australis, yet differing in climatic conditions, offer ideal settings for exploring the broader effects on carbon cycle and climate feedback mechanisms. Monthly observations over an entire growing season revealed that Spartina invasions enhanced the carbon sequestration functions of coastal wetlands in both China and Denmark by increasing carbon dioxide (CO2) sequestration and reducing methane (CH4) emissions. CO2 fluxes in Chinese coastal wetlands were about 10 times higher than those in Denmark, with minimal differences in CH4 emissions. Furthermore, although CH4 emission offset some of the CO2 uptake, the overall radiative balance of Spartina remained lower than that of P. australis, suggesting that Spartina had the potential to mitigate global warming. Species-specific plant traits, like biomass, and abiotic factors, like air and soil temperature, affecting these fluxes in both countries' salt marshes. This study highlighted the intricate interactions between invasive species and carbon dynamics, underscoring the importance of across-regional research to fully understand their role in global climate regulation.