Recovering wetland biogeomorphic feedbacks to restore the world's biotic carbon hotspots

Frequent water table depth fluctuations due to warm-dry conditions can significantly trigger carbon emissions from coastal salt marshes

Coastal salt marshes are crucial for blue carbon storage, but their carbon emission patterns are uncertain due to frequent fluctuations in water table depth (WTD). This uncertainty is caused by the simultaneous impacts of global warming and rising sea levels. This study assessed carbon emission patterns in the Yellow River Delta under different hydrological fluctuation modes (high fluctuation of WTD scenario (HF-WTD) and low fluctuation of WTD scenario (LF-WTD)) and hydrothermal conditions through a 3-year in-situ observational experiment. The region is typically impacted by climatic warming and drying. Results showed that: (i) Intra-annual WTD fluctuations promote CO2 emission flux, but they are not significantly related to the rising or falling state. On the other hand, methane (CH4) emission flux are dominated by WTD that are more favourable when WTD continues to rise. (ii) The transition point for carbon emission flux with respect to WTD is between -51 cm and -54 cm, and is not affected by the fluctuation pattern of the WTD. (iii) CO2 is more sensitive to temperature when the WTD fluctuates violently and is high, while CH4 is more sensitive to temperature when the WTD is stable and low and the temperature is <17.71 °C. (iv) In the scenario of high-frequency WTD, the variation in WTD, combined with the sharp temperature change, contributes to the peak of CO2 emission flux. In contrast, in the low-frequency WTD scenario, WTD fluctuations, coupled with extreme temperature fluctuations, contribute to the peak of CH4 emission flux. The conclusions suggest that the high and frequently fluctuating WTD caused by climate warming and drying, as well as rising sea levels, will significantly increase CO2 emission flux from coastal salt marsh wetlands. This increase in emission flux will be detrimental to the blue carbon function of coastal wetlands.

Dissolved inorganic carbon input significantly lowers carbon dioxide flux but not methane flux in shallow macrophyte-dominated systems with positive effects on carbon stocks

BACKGROUND

With the increase in the inorganic carbon input from watersheds, elevated dissolved inorganic carbon (DIC) concentrations will significantly impact the carbon cycle in freshwater ecosystems. Moreover, the limited diffusion rate of CO2 in water, coupled with the lack of functional stomata, greatly restricts the ability of submerged macrophytes to absorb CO2 from their aquatic environment. The importance of bicarbonate (HCO3-) for submerged macrophytes becomes more pronounced. Current research focuses on the effects of DIC (notably HCO3-) on the phenotypic plasticity of submerged macrophytes, while its impact on their carbon stock capabilities has rarely been reported.

RESULTS

In this study, Myriophyllum spicatum served as the model macrophyte within a mesocosm experimental system to assess the impact of HCO3- enrichment (0.5 to 2.5 mmol L-1) on carbon stocks and emissions across a one-year period. Our findings indicated that the addition of HCO3- had a non-significant inhibitory effect on the diffusive fluxes of methane (CH4) emissions. Concurrently, it significantly reduced CO2 fluxes within the systems. The annual average CO2 fluxes across the four HCO3- addition levels were -3.48 ± 7.60, -6.78 ± 5.87, -7.15 ± 8.68, and -14.04 ± 14.39 mol m-2 yr-1, respectively, showing significant differences between low /medium- and high- HCO3- addition levels.

CONCLUSION

The addition of HCO3- enhanced carbon stocks in water, macrophytes and the entire system, with minimal effects on carbon sedimentation stocks. Our study provides valuable insights into understanding the carbon sink capacity of aquatic ecosystems and elucidates the underlying mechanisms driving these processes on a system scale.

Abundance of microplastics in a typical urban wetland in China: Association with occurrence and carbon storage

Microplastics (MPs) are gaining attention for their widespread presence and toxicity in ecosystems. However, their role as a carbon source in urban wetland carbon sinks is still unclear. In this study, the microplastic-carbon (MP-C) was firstly quantified based on the abundance and occurrence characteristics, including MP morphology, size and type in the Sanyang Wetland, a typical urban wetland of China. MP abundances ranged from 2.4 ± 0.6-14.9 ± 1.5 items/L in surface water and 6.6 ± 1.2 × 103 to 46.3 ± 5.9 × 103 items/kg in sediment. The predominant morphological characterization of MPs was fragments smaller than 200 μm in size, consisting of PP, PE, and PET, which suggests that the main source was domestic wastewater discharge nearby. Notably, in the Sanyang wetland, the contribution of MP-C to total organic carbon (TOC) was estimated to be 0.0230.20 % in water and 0.0260.28 % in sediment. With the continuous production of plastics globally, these values were predicted to increase to 0.12 0.71 % and 0.83 4.12 % by 2100, respectively. Although the estimations relied on simplified geometric assumptions for MP volume and theoretical carbon content, these approaches provide a reasonable basis for understanding MP-C dynamics in wetlands under current analytical constraints. The integration of MP-C characterization during environmental monitoring and management strategies would enhance our understanding of MP pollution's role in the carbon cycle.

Warming-Induced Plant Species Shifts Lead to Substantial Losses of Wetland Soil Carbon

Wetlands are large reservoirs of soil organic carbon (SOC), storing one-third of global SOC within 6% of the land surface. However, the feedback direction and magnitude of wetland SOC storage to climate warming remain unclear. Here we present results from an 8-year (2014-2022) wetland warming experiment in the Yellow River Delta, revealing that wetland SOC storage responds to warming in a phase-dependent manner. We found that warming initially reduced both carbon input and output but did not change SOC storage. However, SOC storage abruptly decreased by 21.4% in 2020, which persisted over the following 2 years. This occurred mainly due to shifts in the biomass of dominant plant species (P. australis) under warming, reducing carbon input, increasing microbial carbon degradation, and resulting in microbial necromass carbon loss. These results highlight the critical role of dominant plant species in driving the wetland soil carbon cycle and its feedback to climate change.

Response of the nosZ-type denitrifying microbial community and metabolic characteristics to precipitation changes in the alpine wetland

The impact of climate change on the global hydrological cycle is becoming increasingly significant, with changes in precipitation patterns emerging as a key factor influencing the carbon and nitrogen cycling processes in alpine wetland ecosystems. However, the response of the nosZ-type denitrifying microbial community and its metabolic characteristics in the source wetland to precipitation changes remains unclear. In this study, high-throughput sequencing of the nosZ gene and LC-MS-based metabolomics were used to investigate the response of the nosZ-type denitrifying microbial community and its metabolic characteristics to precipitation changes (4 years) in the source wetland of Qinghai Lake. The results showed that Microvirga was the key bacterial group in the source wetland of Qinghai Lake, and Azospirillum was sensitive to changes in precipitation (P < 0.05). The 50% rainfall enhancement treatment significantly increased soil moisture, and the total carbon content showed an increasing trend with the increase in precipitation (P < 0.05). pH was the most important explanatory factor for community structure, while total nitrogen content was the key explanatory factor for community diversity. Deterministic processes dominated the assemblage of the nosZ-type denitrifying microbial community in the source wetland of Qinghai Lake. Soil metabolomics analysis showed that the differential metabolites in the Source Wetland mostly exhibited significant positive correlations. Precipitation changes significantly affected the relative abundance of N-Acetylaspartic acid. In summary, lower precipitation is more favorable for maintaining carbon storage in the source wetlands of Qinghai Lake. Precipitation variation disrupted the existing nitrogen balance within the ecosystem and altered the structure of the nosZ-type denitrifying microbial community and soil metabolic characteristics. These findings imply that climate change-driven shifts in precipitation patterns may impact carbon and nitrogen dynamics in alpine wetlands, alter ecosystem stability, and have profound effects on microbial communities and biogeochemical cycles.

Temperature Drives Seagrass Recovery Across the Western North Atlantic

Climate-driven shifts in herbivores, temperature, and nutrient runoff threaten coastal ecosystem resilience. However, ecological resilience, particularly for foundation species, remains poorly understood due to the scarcity of field experiments conducted across appropriate spatial and temporal scales that investigate multiple stressors. This study evaluates the resilience of a widespread tropical marine plant (turtlegrass) to disturbances across its geographic range and examines how environmental gradients in (a)biotic factors influence recovery. We assessed turtlegrass resilience by following recovery rates for a year after a simulated pulse disturbance (complete above- and belowground biomass removal). Contrary to studies in temperate areas, higher temperature generally enhanced seagrass recovery. While nutrients had minimal individual effects, they reduced aboveground recovery when combined with high levels of herbivore grazing (meso and megaherbivore). Belowground recovery was also affected by combined high levels of nutrients and grazing (megaherbivores only). Light availability had minimal effects. Our results suggest that the resilience of some tropical species, particularly in cooler subtropical waters, may initially benefit from warming. However, continuing shifts in nutrient supply and changes in grazing pressure may ultimately serve to compromise seagrass recovery.

Impact of salinity gradients on nitric oxide emissions and functional microbes in estuarine wetland sediments

Estuarine wetland sediments are hotspots for nitrogen cycling and critical sources of atmospheric nitric oxide (NO). Yet studies on the impact of sediment salinity gradients on NO emissions and associated functional microbes at the land-ocean interface remain limited. Here, we measured sediment NO emission rates from incubated sediment samples that were collected from an estuarine wetland in Qingdao, China. Our findings indicate that sediment salinity is a pivotal factor shaping NO emission rates, by altering the community composition and gene abundance of functional microbes involved in NO emissions, with rates ranging from 0.04 to 0.25 μg N kg-1 dry soil h-1. Metagenomic analysis of the sediment samples reveals that greater NO emission rates (+486 %) under salinity changes are linked to a higher abundance of the nirS gene (+26 %) responsible for NO formation and a lower abundance of norBC genes (-23 %) responsible for NO consumption. Accordingly, the increase of NO emissions may be attributed to the accumulation of denitrifying NO, which could improve plant salt tolerance through co-evolutionary interactions between plants and sediment-dwelling microbes. Taken together, these findings contribute to a richer understanding of how biochemical NO emissions in estuarine wetland sediments respond to salinity gradients.

Assessing environmental gradients in relation to dark CO2 fixation in estuarine wetland microbiomes

The rising atmospheric concentration of CO2 is a major concern to society due to its global warming potential. In soils, CO2-fixing microorganisms are preventing some of the CO2 from entering the atmosphere. Yet, the controls of dark CO2 fixation are rarely studied in situ. Here, we examined the gene and transcript abundance of key genes involved in microbial CO2 fixation along major environmental gradients within estuarine wetlands. A combined multi-omics approach incorporating metabarcoding, deep metagenomic, and metatranscriptomic analyses confirmed that wetland microbiota harbor four out of seven known CO2 fixation pathways, namely, the Calvin cycle, reverse tricarboxylic acid cycle, Wood-Ljungdahl pathway, and reverse glycine pathway. These pathways are transcribed at high frequencies along several environmental gradients, albeit at different levels depending on the environmental niche. Notably, the transcription of the key genes for the reverse tricarboxylic acid cycle was associated with high nitrate concentration, while the transcription of key genes for the Wood-Ljungdahl pathway was favored by reducing, O2-poor conditions. The transcript abundance of the Calvin cycle was favored by niches high in organic matter. Taxonomic assignment of transcripts implied that dark CO2 fixation was mainly linked to a few bacterial phyla, namely, Desulfobacterota, Methylomirabilota, Nitrospirota, Chloroflexota, and Pseudomonadota.

IMPORTANCE

The increasing concentration of atmospheric CO2 has been identified as the primary driver of climate change and poses a major threat to human society. This work explores the mostly overlooked potential of light-independent CO2 fixation by soil microbes (a.k.a. dark CO2 fixation) in climate change mitigation efforts. Applying a combination of molecular microbial tools, our research provides new insights into the ecological niches where CO2-fixing pathways are most active. By identifying how environmental factors, like oxygen, salinity and organic matter availability, influence these pathways in an estuarine wetland environment, potential strategies for enhancing natural carbon sinks can be developed. The importance of our research is in advancing the understanding of microbial CO2 fixation and its potential role in the global climate system.

Increased but not pristine soil organic carbon stocks in restored ecosystems

Ecosystem restoration can contribute to climate change mitigation, as recovering ecosystems sequester atmospheric CO2 in biomass and soils. It is, however, unclear how much soil organic carbon (SOC) stocks recover across different restored ecosystems. Here, we show SOC recovery in different contexts globally by consolidating 41 meta-analyses into a second-order meta-analysis. We find that restoration projects have, since their inception, led to significant SOC increases compared to the degraded state in 12 out of 16 ecosystem-previous land-use combinations, with mean SOC increases thus far that range from 25% (grasslands; 10-39%, 95% CI) to 79% (shrublands; 38-120% CI). Yet, we observe a SOC deficit in restored ecosystems compared to pristine sites, ranging from 14% (forests; 12-16% CI) to 50% (wetlands; 14-87% CI). While restoration does increase carbon sequestration in SOC, it should not be viewed as a way to fully offset carbon losses in natural ecosystems, whose conservation has priority.

Increased Mineral-Associated Organic Carbon and Persistent Molecules in Allochthonous Blue Carbon Ecosystems

Coastal wetlands contain very large carbon (C) stocks-termed as blue C-and their management has emerged as a promising nature-based solution for climate adaptation and mitigation. The interactions among sources, pools, and molecular compositions of soil organic C (SOC) within blue C ecosystems (BCEs) remain elusive. Here, we explore these interactions along an 18,000 km long coastal line of salt marshes, mangroves, and seagrasses in China. We found that mineral-associated organic C (MAOC) is enriched in BCEs dominated by allochthonous inputs and abundant active minerals, leading to an increased proportion of persistent organic molecules. Specifically, soils with large allochthonous inputs (> 50%) are characterized by a substantial contribution of MAOC (> 70%) to total SOC with a notable preservation of lipids (36%) across salt marshes, mangroves, and seagrasses. The burial of allochthonous particles, derived from external sources such as rivers or tidal influxes, facilitates the formation of stable MAOC through binding to mineral surfaces or occlusion within microaggregates. The proportions of particulate organic C (POC) and MAOC are important predictors for molecular compositions of soil organic matter. Lipid proportions within molecular composition decrease as POC and autochthonous C proportions increase. These findings provide new insights into the coupled control over SOC sequestration in BCEs, emphasizing the role of allochthonous inputs, proportions of carbon pools, and persistent organic components.

Increased sea level rise accelerates carbon sequestration in a macro-tidal salt marsh

Salt marshes are known as key ecosystems for nature-based climate mitigation through organic carbon sequestration into their sediment beds, but at the same time they are affected by accelerating sea level rise induced by climate warming. Consequently, an important question is how organic carbon accumulation rates (OCAR) of salt marshes will respond to future accelerating rates of relative sea level rise (RSLR). To date, existing insights are either based on (1) comparison of geographically distant marsh sites, differing in local RSLR rates but also in other environmental conditions that additionally can affect OCAR, or (2) experiments in given marsh sites, in which proxies for RSLR are manipulated, but run over periods of years instead of decades, the latter being the relevant time scale of marsh responses to RSLR. Here we bridge these shortcomings by studying the OCAR over four decades at two nearby salt marsh sites in the Netherlands, with similar environmental conditions, but with one site experiencing an accelerated RSLR rate of 9.7-11.7 mm yr-1 (i.e., within the range of projected global mean sea level rise rates by 2100) due to local land subsidence induced by gas extraction, while the other site does not experience subsidence and has a low background RSLR rate of 2.0 mm yr-1 (i.e. close to the current global mean sea level rise rate). Our results reveal that the salt marsh site experiencing the accelerated RSLR rates shows OCAR values that are on average twice as high as those found in the marsh site experiencing the low background RSLR rates. Moreover, the increase of OCAR in response to faster RSLR was even more pronounced (i.e. 63 % increase) on marsh levees within 10 m from tidal creeks, while this was more subtle (i.e. 27 % increase) in marsh basins at a distance of 30-40 m from the creeks. These observations of increased OCAR are mainly attributed to increased sediment accretion rates (SAR) in response to (1) increased tidal inundation due to accelerated RSLR and (2) larger sediment supply due to closer proximity to creeks, while sediment organic carbon content was relatively little affected. Our findings support expectations that nature-based climate mitigation actions, through salt marsh conservation and restoration, are sustainable on the long term of the coming decades, and are even likely to become more effective with future accelerations in global sea level rise, at least for macrotidal sites not limited by sediment supply.

Wetland vegetation zoning as a response to groundwater complex systems

This research investigates the interplay between groundwater flow systems and the zoning of wetland species. We aimed to elucidate the relationship between these factors through comprehensive field evaluations encompassing plant composition, piezometric levels, and flow direction; groundwater chemistry, vertical and horizontal, at different depths (0.15 m, 2 m, 4 m, and 6 m) during both rainy and dry seasons. Our findings reveal distinct patterns. The plant diversity in the FP site was related to low ion concentration. In contrast, the dominance of T. geniculata in the TH site correlated with species adapted to sulfate and chloride (SO42- and Cl-) tolerance. In the CTC site, the dominance of C. jamaicense was linked to local groundwater flow and significant surface water inflows. At the same time, T. domingensis prevailed in the TC site due to sodium chloride facie inhibiting C. jamaicense seed germination. Our study highlights the role of groundwater chemical composition in shaping wetland ecosystems by influencing species tolerance and how the spatial distribution of groundwater discharge and seasonal changes contribute to distinct vegetation patches within wetlands. The relationship between groundwater systems, the water's chemical composition, and vegetation is strongly dependent. This can explain mortality and changes in vegetation composition in wetlands in different parts of the world, stressed by climate change effects (rain pattern alteration).

SDG space: Revealing the structure and complementarities among sustainable development goals in China

To achieve the United Nations Sustainable Development Goals (SDGs) by 2030, it is essential to understand the interlinkages between the goals. Previous research has investigated these interactions by focusing on their correlations. However, few studies have systematically prioritized them from a structural perspective through the complementarity measurements and empirically validated their policy effectiveness, such as which goals and indicators impact other SDGs most, especially in China. This study introduces a new concept known as the 'SDG space' by employing the "Product Space" approach in network science and economics. It measures the complementarities between SDGs and indicators through their network structures in investigating effective policy design. Using the most recent available but unpublished data for 31 Chinese provinces, the SDG space was constructed at the 17 SDG and 118 indicator levels by analyzing the probability of comparative advantage between each SDG or indicator pair co-occurring in the same place. Historical data confirm that in the 'SDG Space' network, a goal connected to other well-developed goals would enjoy better future growth and vice versa. The structure reveals that SDG 4 (Quality Education), 15 (Life on Land), and 1 (No Poverty) are critical goals with transformative synergies to other SDGs. Furthermore, we identified strong complementarities between land-based ecosystems and clean water and climate actions using the finer-grained indicator-level space. These findings help pave the way for China toward a sustainable future by providing science-based policy recommendations for decision-makers. They can be generally applied to other countries and regions to assist in navigating toward sustainable development.

Mass concentrations, compositions and burial fluxes of nano- and micro-plastics in a multi-species saltmarsh

Plastic pollution poses a serious threat to marine ecosystems; yet quantifying the mass concentrations of nano- and microplastics (NMPs) in saltmarsh sediments at the ocean-land interface remains a critical research gap. Here, the study employed reliable and efficient analytical techniques, namely pressurized liquid extraction and the double-shot model of thermal desorption/pyrolysis-gas chromatography-mass spectrometry, to quantify six different types of NMPs in the sediment of a multi-species saltmarsh, providing the first comprehensive assessment of NMP mass concentration and burial in this saltmarsh environment. The results demonstrate that polyethylene, polyvinyl chloride, and polypropylene dominated the NMP composition in sediments, constituting 72.6%, 17.3%, and 4.5% of the total NMPs, respectively. The measured NMPs represent an anthropogenic intrusion, constituting 0.10%-0.23% of the carbon storage in the saltmarsh. By examining the vertical concentration profiles, this study unveiled the influence of saltmarsh vegetation on NMP deposition in sediments, establishing a connection with local sedimentation patterns and the historical zonation of plant species such as Scirpus mariqueter, Phragmites australis and Spartina alterniflora. These findings underscore the crucial role of saltmarsh vegetation in facilitating NMP settling and retention, highlighting the necessity of considering vegetation dynamics in examining the emerging NMP pollution in coastal wetlands.

Spatial distribution of soil organic carbon across diverse vegetation types in a tidal wetland

Tidal wetlands are significant contributors to global "blue carbon" resources. The water and salt gradients in tidal wetlands shape vegetation distribution and store significant amounts of soil organic carbon (SOC). We selected four distinct regions within the intertidal zone comprising three distinct vegetation types: low-tide saltmarsh Suaeda salsa (LS), high-tide saltmarsh Suaeda salsa (HS), mid-high-tide Phragmites australis (P), and high-tide Tamarix chinensis (T). Through field sampling and indoor analysis, we found significant differences in SOC levels across various vegetation types along the land-sea gradient. Among these, LS exhibited the highest SOC levels, while P had the lowest. Additionally, there were vertical variations of SOC within a 1-m range among different vegetation types. Mantel analysis and SEM demonstrated that SWC influences SOC content by manipulating vegetation types, thereby regulating total soil carbon. Overall, our findings provide valuable insights for further investigating the effects of vegetation succession on soil carbon pool evolution.

Optimization of Electromagnetic-Wave Reflectivity Performance of Electromagnetic Shielding Yarn Prepared by Evaporation-Induced Sintering of Ga60.5In25Sn13Zn1.5 Alloy with Nanosilicates

Electromagnetic interference (EMI) shielding textiles have received widespread attention, and liquid metal (LM) shows superiority in flexible and deformable electronics. Here, we introduce a novel method using nanosilicates to help sinter LM through capillary evaporation, resulting in strong adhesion to substrates. By adjustment of the amount of nanosilicates, flexible EMI shielding yarns are created using dip-coating and curing processes. The sintered LM tightly adhered to the undulating and uneven surfaces of polyurethane (PU) yarns. The as-fabricated ION/LM@PU ("ION" is abbreviation of "ionogel") has strong EMI shielding and low EM-wave reflection due to the high electrical conductivity of the LM layer and good impedance matching of P(AAm-co-AA) ionogel. The addition of an ionogel enhances EM-wave absorption and strengthens interfacial polarization, making it an effective green EMI shielding yarn for reducing secondary reflection pollution. ION/LM@PU exhibited high total electromagnetic interference shielding effectiveness (EMI SET) (∼56 dB), low reflected power coefficient (R) (∼0.153), high impedance matching (|Zin/Z0| ≈ 0.660), high tensile strength (∼23.75 MPa), and high elastic recovery (∼0.92 at 10th stretch-release cycle). The EMI shielding mechanism of ION/LM@PU ± 60° is composed of reflective loss and absorption loss (including multireflective loss, conduction loss, dipole polarization loss, and interfacial polarization loss).

Spatial variability in blue carbon storage and sequestration of seagrass meadows in southern China

Although seagrass meadows are intense carbon sinks, information on the regional variability in seagrass blue carbon stocks and carbon sequestration remains limited. We estimated the organic carbon (Corg) stocks and carbon accumulation rates (CAR) of seven seagrass meadows along the subtropical coast of China's Zhanjiang City and analyzed the driving factors of variability in sediment Corg stocks in three seagrass meadows. Results showed that most Corg (99.83 %) was stored in the sediments, and the contribution of living biomass was minor. The average Corg stocks of living biomass and sediments across all sites were 0.04 ± 0.01 and 42.03 ± 25.07 Mg C ha-1, respectively, which were significantly lower than the world average (2.52 ± 0.48 and 194.2 Mg C ha-1). The sediment Corg stocks of the upper 1 m ranged from 24.26 to 157.12 Mg C ha-1 with substantial variability among sites: Liusha Bay (64.93 ± 22.31 Mg C ha-1) > Donghai Island (33.8 ± 10.65 Mg C ha-1) > Dongshen Ferry (27.35 ± 4.15 Mg C ha-1). The average sediment CAR was 53.47 g C m-2 yr-1, and the total CAR of 864.18 ha seagrass meadows was 260.76 ± 4.86 Mg C yr-1 in these studied sites. Physicochemical factors, such as high moisture content, salinity, CaCO3 content, and low dry bulk density, jointly inhibited the mineralization rate of Corg in sediments. Our study provides data from understudied regions to a growing dataset on seagrass carbon stocks and sequestration rates and highlights the significance of local and regional differences in seagrass blue carbon storage to accurately assess the climate change mitigation potential of seagrass ecosystems.

Metallic protection of soil carbon: divergent drainage effects in Sphagnum vs. non-Sphagnum wetlands

The established paradigm assumes that drainage may decrease the vast soil organic carbon (SOC) reservoir in global wetlands. Yet drainage can also promote SOC stabilization by fostering the accrual of metal-bound organic carbon (bound OC) upon oxygen exposure. Here, this emergent mechanism is tested for the first time at a regional scale, using literature data and a nationwide, pairwise survey of drained wetlands across China. We show that long-term (15-55 years) drainage largely increased metallic protection of SOC (bound OC%) in non-Sphagnum wetlands, but consistently decreased bound OC% in Sphagnum wetlands following replacement of the 'rust engineer' Sphagnum by herbaceous plants. Improved SOC stock estimates based on 66 soil profiles reveal that bound OC increases can compensate for the loss of unbound SOC components in non-Sphagnum wetlands with substantial accrual of reactive metals. Metallic stabilization of wetland SOC is hence a widespread but overlooked mechanism that is heavily influenced by vegetational shifts. Incorporating this novel mechanism into models will improve prediction of wetland SOC dynamics under shifting hydrological regimes.

Water quality and microbial interaction network topological parameters were the key factors affecting litter decomposition under wetland restoration

Wetland restoration has a significantly impacts biogeochemical cycles. However, the specific mechanisms and potential microbial processes by which wetland restoration influences litter decomposition remain unclear. This knowledge gap hinders our ability to accurately predict ecological processes within wetland ecosystems across various restoration timeframes. Therefore, we conducted an in situ experiment was conducted in wetlands in Northeast China using the litterbag method, involving a restoration time gradient. Natural wetlands served as controls, with wetlands restored for 17 years (R17), 3 years (R3), 2 years (R2), and 1 year (R1). The study focused on two typical wetland plants: reed (Phragmites australis) and sedge (Cyperus rotundus), to investigate the effects of wetland restoration on microbial community, as well as the decomposition of litter. During the experiment, the decomposition rates (k-values) of both types of litter were lower in restored wetlands than natural wetlands. Fungal diversity varied significantly between restored and natural wetlands. In the short term (R3), the community structures of bacteria and fungi in restored wetlands resembled those of natural wetlands. However, significant differences persisted in long-term restored wetlands (R17). Partial Least Squares Path Modeling (PLS-PM) revealed that bacterial network cohesion (network average density, network transitivity) and wetland restoration time are the primary drivers of Reed and Sedge litter decomposition. Overall, wetland restoration enhances litter decomposition by altering the physicochemical properties of water and the characteristics of the microbial interaction network, suggesting that wetland restoration can accelerate the material cycling processes within wetland ecosystems.

Responses of CO2 and CH4 in the alpine wetlands of the Tibetan Plateau to warming and nitrogen and phosphorus additions

Wetland ecosystems store large amounts of carbon, and CO2 and CH4 fluxes from this ecosystem receive the double impact of climate change and human activities. Nonetheless, research on how multi-gradient warming and nitrogen and phosphorus additions affect these wetland greenhouse gas emissions is still limited, particularly in alpine wetland ecosystems. Therefore, we conducted a field experiment on the Tibetan Plateau wetlands, investigating the effects of warming and nitrogen and phosphorus additions on the CO2 and CH4 fluxes in alpine wetlands. Results indicated that warming enhanced the CO2 absorption and CH4 emission in the alpine meadow ecosystem, possibly related to changes in plant growth and microbial activity induced by warming, while we noticed that the promotion of CO2 uptake weakened with the increase in the magnitude of warming, suggesting that there may be a temperature threshold beyond which the ecosystem's capacity for carbon sequestration may be reduced. Nitrogen addition increased CH4 emission, with the effect on CO2 absorption shifting from inhibition to enhancement as the amount of applied nitrogen or phosphorus increased. The interaction between warming and nitrogen and phosphorus additions further influenced CH4 emission, exhibiting a synergistic enhancement effect. This study deepens our understanding of the greenhouse gas responses of alpine wetland ecosystems to warming and nitrogen and phosphorus additions, which is significant for predicting and managing ecosystem carbon balance under global change.

Elevating water table reduces net ecosystem carbon losses from global drained wetlands

Drained wetlands are thought to be carbon (C) source hotspots, and rewetting is advocated to restore C storage in drained wetlands for climate change mitigation. However, current assessments of wetland C balance mainly focus on vertical fluxes between the land and atmosphere, frequently neglecting lateral carbon fluxes and land-use effects. Here, we conduct a global synthesis of 893 annual net ecosystem C balance (NECB) measures that include net ecosystem exchange of CO2, along with C input via manure fertilization, and C removal through biomass harvest or hydrological exports of dissolved organic and inorganic carbon, across wetlands of different status and land uses. We find that elevating water table substantially reduces net ecosystem C losses, with the annual NECB decreasing from 2579 (95% interval: 1976 to 3214) kg C ha-1 year-1 in drained wetlands to -422 (-658 to -176) kg C ha-1 year-1 in natural wetlands, and to -934 (-1532 to -399) kg C ha-1 year-1 in rewetted wetlands globally. Climate, land-use history, and time since water table changes introduce variabilities, with drainage for (sub)tropical agriculture or forestry uses showing high annual C losses, while the net C losses from drained wetlands can continue to affect soil C pools for several decades. Rewetting all types of drained wetlands is needed, particularly for those formerly agriculture-used (sub)tropical wetlands where net ecosystem C losses can be largely reduced. Our findings suggest that elevating water table is an important initiative to reduce C losses in degraded wetlands, which could contribute to policy decisions for managing wetlands to enhance their C sequestration.

Four decades of data indicate that planted mangroves stored up to 75% of the carbon stocks found in intact mature stands

Mangroves' ability to store carbon (C) has long been recognized, but little is known about whether planted mangroves can store C as efficiently as naturally established (i.e., intact) stands and in which time frame. Through Bayesian logistic models compiled from 40 years of data and built from 684 planted mangrove stands worldwide, we found that biomass C stock culminated at 71 to 73% to that of intact stands ~20 years after planting. Furthermore, prioritizing mixed-species planting including Rhizophora spp. would maximize C accumulation within the biomass compared to monospecific planting. Despite a 25% increase in the first 5 years following planting, no notable change was observed in the soil C stocks thereafter, which remains at a constant value of 75% to that of intact soil C stock, suggesting that planting effectively prevents further C losses due to land use change. These results have strong implications for mangrove restoration planning and serve as a baseline for future C buildup assessments.

Marsh decrease was much faster than the water increase among the Yellow River Source wetlands during 1986-2022

Wetlands are valuable and sensitive ecosystems that make them imperative to tracking the dynamics in their extent for sustainable management under global warming. Here we focused on the Yellow River Source (YRS) wetlands, which is renowned for hosting one of the world's largest plateau peat bog, unfortunately, it had experienced sharp degradation, threatening the safety of water supply for approximately 110 million people of the lower Yellow River basin. However, the lack of long-term, dense time-series data makes it challenging to assess its evolution trends and driving factors. Therefore, we developed a decision tree sample migration method based on Euclidean distance and Land Surface Water Index, and successfully generated annual wetland mapping of YRS from 1986 to 2022 by utilizing the Landsat 5/7/8 datasets and Random Forest method. The average sample migration rate was 89.21 %, with an average overall accuracy of 95.49 %. We observed that the marsh area decreased by 2031 km2, marking a decline of 12.98 %, while the water area increased by 710 km2 (31.24 %) compared to 1986. Spatially, 10.96 % of marsh composition presents significant (P < 0.05) decline trend, which are mainly converted to grass (86 %), followed by impervious (10 %). There were 6.69 % of water composition showing significant (P < 0.05) increase trend, which are mainly sourced from impervious (82 %) and marsh (12 %). Grazing activities were more important driving forces than climate change for marsh degradation, while the water expansion was associated with recent rising temperature in YRS. The sample migration method is proved to be feasible, robust, and effective for long-term wetland mapping. We suggest that wetland decision-makers need to focus on marsh degradation and reduce grazing intensity, so that fostering the sustainable and healthy wetlands in the Qinghai-Tibetan Plateau.

miR397 regulates cadmium stress response by coordinating lignin polymerization in the root exodermis in Kandelia obovata

Secondary lignification of the root exodermis of Kandelia obovata is crucial for its response to adversity such as high salinity and anaerobic environment, and this lignification is also effective in blocking cadmium transport to the roots. However, how the differences in lignification of root exodermis at different developmental stages respond to Cd stress and its regulatory mechanisms have not been revealed. In this study, after analyzing the root structure and cell wall thickness using a Phenom scanning electron microscope as well as measuring cadmium content in the root cell wall, we found that the exodermis of young and mature roots of K. obovata responded to Cd stress through the polymerization of different lignin monomers, forming two different mechanisms: chelation and blocking. Through small RNA sequencing, RLM-5'-RACE and dual luciferase transient expression system, we found that miR397 targets and regulates KoLAC4/17/7 expression. The expression of KoLAC4/17 promoted the accumulation of guaiacyl lignin during lignification and enhanced the binding of cadmium to the cell wall. Meanwhile, KoLAC7 expression promotes the accumulation of syringyl lignin during lignification, which enhances the obstruction of cadmium and improves the tolerance to cadmium. These findings enhance our understanding of the molecular mechanisms underlying the differential lignification of the root exodermis of K. obovata in response to cadmium stress, and provide scientific guidance for the conservation of mangrove forests under heavy metal pollution.

Organic carbon accumulation in British saltmarshes

Saltmarshes are a crucial component of the coastal carbon (C) system and provide a natural climate regulation service through the accumulation and long-term storage of organic carbon (OC) in their soils. These coastal ecosystems are under growing pressure from a changing climate and increasing anthropogenic disturbance. To manage and protect these ecosystems for C and to allow their inclusion in emissions and natural-capital accounting, as well as carbon markets, accurate and reliable estimates of OC accumulation are required. However, globally, such data are rare or of varying quality. Here, we quantify sedimentation rates and OC densities for 21 saltmarshes in Great Britain (GB). We estimate that, on average, saltmarshes accumulate OC at a rate of 110.88 ± 43.12 g C m-2 yr-1. This is considerably less than widely applied global saltmarsh averages. It is therefore highly likely that the contribution of northern European saltmarshes to global saltmarsh OC accumulation has been significantly overestimated. Taking account of the climatic, geomorphological, oceanographic, and ecological characteristics of all GB saltmarshes and the areal extent of different saltmarsh zones, we estimate that the 451.65 km2 of GB saltmarsh accumulates 46,563 ± 4353 t of OC annually. These low OC accumulation rates underline the importance of the 5.20 ± 0.65 million tonnes of OC already stored in these vulnerable coastal ecosystems. Going forward the protection and preservation of the existing stores of OC in GB saltmarshes must be a priority for the UK as this will provide climate benefits through avoided emissions several times more significant than the annual accumulation of OC in these ecosystems.

A global meta-analysis on the drivers of salt marsh planting success and implications for ecosystem services

Planting has been widely adopted to battle the loss of salt marshes and to establish living shorelines. However, the drivers of success in salt marsh planting and their ecological effects are poorly understood at the global scale. Here, we assemble a global database, encompassing 22,074 observations reported in 210 studies, to examine the drivers and impacts of salt marsh planting. We show that, on average, 53% of plantings survived globally, and plant survival and growth can be enhanced by careful design of sites, species selection, and novel planted technologies. Planting enhances shoreline protection, primary productivity, soil carbon storage, biodiversity conservation and fishery production (effect sizes = 0.61, 1.55, 0.21, 0.10 and 1.01, respectively), compared with degraded wetlands. However, the ecosystem services of planted marshes, except for shoreline protection, have not yet fully recovered compared with natural wetlands (effect size = -0.25, 95% CI -0.29, -0.22). Fortunately, the levels of most ecological functions related to climate change mitigation and biodiversity increase with plantation age when compared with natural wetlands, and achieve equivalence to natural wetlands after 5-25 years. Overall, our results suggest that salt marsh planting could be used as a strategy to enhance shoreline protection, biodiversity conservation and carbon sequestration.

Vegetation types and flood water level are dominant factors controlling the carbon sequestration potential in Dongting Lake floodplain, China

Wetlands are important carbon sinks. However, the carbon sequestration potential of flooded wetlands may be weakened owing to water regime changes induced by anthropogenic disturbances. Using the eddy covariance technique, this study quantified the effects of the water level and vegetation types on the net ecosystem CO2 exchange (NEE), gross primary production (GPP), and ecosystem respiration (Reco) from a reed marsh (Miscanthus sacchariflorus) and a sedge meadow (Carex spp.) in the Dongting Lake floodplain from 2014 to 2016. Our results indicated that the sedge meadow (-89.49 to -186.47 g C m-2 y-1) and reed marsh (-246.12 to -513.94 g C m-2 y-1) were carbon sinks on the interannual timescale. However, the sedge meadow changed from a carbon sink to a carbon source during the flooding season. The effect of flooding on the carbon sink function in the reed marsh was dependent on the water level. The carbon sink function of the reed marsh was enhanced by moderate flooding (water level under 30.5 m in Chenglingji) owing to the inhibition of Reco, but was weakened by extremely high-water levels (over 33 m in Chenglingji) during the flooding season. Seasonal variations in NEE, GPP, and Reco were closely related to photosynthetic photon flux density, soil water content, water level, soil temperature, and air temperature. We can conclude that the increase in reed area combined with the decrease in flooding days in the sedge meadow can potentially enhance the carbon sink function of the Dongting Lake floodplain.

A meta-analysis reveals increases in soil organic carbon following the restoration and recovery of croplands in Southwest China

In China, the Grain for Green Program (GGP) is an ambitious project to convert croplands into natural vegetation, but exactly how changes in vegetation translate into changes in soil organic carbon remains less clear. Here we conducted a meta-analysis using 734 observations to explore the effects of land recovery on soil organic carbon and nutrients in four provinces in Southwest China. Following GGP, the soil organic carbon content (SOCc) and soil organic carbon stock (SOCs) increased by 33.73% and 22.39%, respectively, compared with the surrounding croplands. Similarly, soil nitrogen increased, while phosphorus decreased. Outcomes were heterogeneous, but depended on variations in soil and environmental characteristics. Both the regional land use and cover change indicated by the landscape type transfer matrix and net primary production from 2000 to 2020 further confirmed that the GGP promoted the forest area and regional mean net primary production. Our findings suggest that the GGP could enhance soil and vegetation carbon sequestration in Southwest China and help to develop a carbon-neutral strategy.

Climate change will reduce North American inland wetland areas and disrupt their seasonal regimes

Climate change can alter wetland extent and function, but such impacts are perplexing. Here, changes in wetland characteristics over North America from 25° to 53° North are projected under two climate scenarios using a state-of-the-science Earth system model. At the continental scale, annual wetland area decreases by ~10% (6%-14%) under the high emission scenario, but spatiotemporal changes vary, reaching up to ±50%. As the dominant driver of these changes shifts from precipitation to temperature in the higher emission scenario, wetlands undergo substantial drying during summer season when biotic processes peak. The projected disruptions to wetland seasonality cycles imply further impacts on biodiversity in major wetland habitats of upper Mississippi, Southeast Canada, and the Everglades. Furthermore, wetlands are projected to significantly shrink in cold regions due to the increased infiltration as warmer temperature reduces soil ice. The large dependence of the projections on climate change scenarios underscores the importance of emission mitigation to sustaining wetland ecosystems in the future.

Surface engineering for stable electrocatalysis

In recent decades, significant progress has been achieved in rational developments of electrocatalysts through constructing novel atomistic structures and modulating catalytic surface topography, realizing substantial enhancement in electrocatalytic activities. Numerous advanced catalysts were developed for electrochemical energy conversion, exhibiting low overpotential, high intrinsic activity, and selectivity. Yet, maintaining the high catalytic performance under working conditions with high polarization and vigorous microkinetics that induce intensive degradation of surface nanostructures presents a significant challenge for commercial applications. Recently, advanced operando and computational techniques have provided comprehensive mechanistic insights into the degradation of surficial functional structures. Additionally, various innovative strategies have been devised and proven effective in sustaining electrocatalytic activity under harsh operating conditions. This review aims to discuss the most recent understanding of the degradation microkinetics of catalysts across an entire range of anodic to cathodic polarizations, encompassing processes such as oxygen evolution and reduction, hydrogen reduction, and carbon dioxide reduction. Subsequently, innovative strategies adopted to stabilize the materials' structure and activity are highlighted with an in-depth discussion of the underlying rationale. Finally, we present conclusions and perspectives regarding future research and development. By identifying the research gaps, this review aims to inspire further exploration of surface degradation mechanisms and rational design of durable electrocatalysts, ultimately contributing to the large-scale utilization of electroconversion technologies.

Nitrogen fertilization enhances organic carbon accumulation in topsoil mainly by improving photosynthetic C assimilation in a salt marsh

Continuous nitrogen (N) loading alters plant growth and subsequently has the potential to impact soil organic carbon (SOC) accumulation in salt marshes. However, the knowledge gap of photosynthesized carbon (C) allocation in plant-soil-microbial systems hampers the quantification of C fluxes and the clarification of the mechanisms controlling the C budget under N loading in salt marsh ecosystems. To address this, we conducted an N fertilization field observation combined with a 5 h 13C-pulse labeling experiment in a salt marsh dominated by Suaeda. salsa (S. salsa) in the Yellow River Delta (YRD), China. N fertilization increased net 13C assimilation of S. Salsa by 277.97%, which was primarily allocated to aboveground biomass and SOC. However, N fertilization had little effect on 13C allocation to belowground biomass. Correlation analysis showed that 13C incorporation in soil was significantly and linearly correlated with 13C incorporation in shoots rather than in roots both in a 0 N (0 g N m-2 yr-1) and +N (20 g N m-2 yr-1) group. The results suggested that SOC increase under N fertilization was mainly due to an increased C assimilation rate and more efficient downward transfer of photosynthesized C. In addition, N fertilization strongly improved the 13C amounts in the chloroform-labile SOC component by 295.26%. However, the absolute increment of newly fix 13C mainly existed in the form of residual SOC, which had more tendency for burial in the soil. Thus, N fertilization enhanced SOC accumulation although C loss increased via belowground respiration. These results have important implications for predicting the carbon budget under further human-induced N loading.

Climate warming enhances microbial network complexity by increasing bacterial diversity and fungal interaction strength in litter decomposition

Microbial communities are important drivers of plant litter decomposition; however, the mechanisms of microbial co-occurrence networks and their network interaction dynamics in response to climate warming in wetlands remain unclear. Here, we conducted a 1.5-year warming experiment on the bacterial and fungal communities involved in litter decomposition in a typical wetland. The results showed that warming accelerated the decomposition of litter and had a greater effect on the diversity of bacteria than on that of fungi. Dominant bacterial communities, such as Bacteroidia, Alphaproteobacteria, and Actinobacteria, and dominant fungal communities, such as Leotiomycetes and Sordariomycetes, showed significant positive correlations with lignin and cellulose. Co-occurrence networks revealed that the average path length and betweenness centrality under warming conditions increased in the bacterial community but decreased in the fungal community. Both bacterial and fungal networks in the 2.0 °C warming treatment had the highest ratio of positive links (58.53 % and 98.14 %), indicating that moderate warming can promote the positive correlations and symbiotic relationships observed in the microbial community. This also suggests that small-world characteristics and weak-link advantages accelerate diffusion, and scale-free features facilitate propagation in microbial communities in response to climate warming. Logistic growth and Lotka-Volterra competition models revealed that climate warming enhances microbial network complexity mainly by increasing bacterial diversity and fungal interaction strength in litter decomposition. However, the symbiotic relationship decreased slightly under 4.0 °C warming, indicating that climate warming is a random attack rather than a targeted attack, and the microbial network has strong resistance to random attack, as shown by the highly robust dynamic performance of the microbial network in litter decomposition. Overall, the microbial community in litter decomposition responded to climate warming and shifted its network interactions, leading to further changes in emergent network topology and dynamics, thus accelerating litter decomposition in wetlands.

A global analysis of how human infrastructure squeezes sandy coasts

Coastal ecosystems provide vital services, but human disturbance causes massive losses. Remaining ecosystems are squeezed between rising seas and human infrastructure development. While shoreline retreat is intensively studied, coastal congestion through infrastructure remains unquantified. Here we analyse 235,469 transects worldwide to show that infrastructure occurs at a median distance of 392 meter from sandy shorelines. Moreover, we find that 33% of sandy shores harbour less than 100 m of infrastructure-free space, and that 23-30% of this space may be lost by 2100 due to rising sea levels. Further analyses show that population density and gross domestic product explain 35-39% of observed squeeze variation, emphasizing the intensifying pressure imposed as countries develop and populations grow. Encouragingly, we find that nature reserves relieve squeezing by 4-7 times. Yet, at present only 16% of world's sandy shores have a protected status. We therefore advocate the incorporation of nature protection into spatial planning policies.

More is not always better: peat moss mixtures slightly enhance peatland stability

Terrestrial wetland ecosystems challenge biodiversity-ecosystem function theory, which generally links high species diversity to stable ecosystem functions. An open question in ecosystem ecology is whether assemblages of co-occurring peat mosses contribute to the stability of peatland ecosystem processes. We conducted a two-species (Sphagnum cuspidatum, Sphagnum medium) replacement series mesocosm experiment to evaluate the resistance, resilience, and recovery rates of net ecosystem CO2 exchange (NEE) under mild and deep water table drawdown. Our results show a positive effect of mild water table drawdown on NEE with no apparent role for peat moss mixture. Our study indicates that the carbon uptake capacity by peat moss mixtures is rather resilient to mild water table drawdown, but seriously affected by deeper drought conditions. Co-occurring peat moss species seem to enhance the resilience of the carbon uptake function (i.e. ability of NEE to return to pre-perturbation levels) of peat moss mixtures only slightly. These findings suggest that assemblages of co-occurring Sphagnum mosses do only marginally contribute to the stability of ecosystem functions in peatlands under drought conditions. Above all, our results highlight that predicted severe droughts can gravely affect the sink capacity of peatlands, with only a small extenuating role for peat moss mixtures.

A unified explanation for the morphology of raised peatlands

Raised peatlands, or bogs, are gently mounded landforms that are composed entirely of organic matter1-4 and store the most carbon per area of any terrestrial ecosystem5. The shapes of bogs are critically important because their domed morphology4,6,7 accounts for much of the carbon that bogs store and determines how they will respond to interventions8,9 to stop greenhouse gas emissions and fires after anthropogenic drainage10-13. However, a general theory to infer the morphology of bogs is still lacking4,6,7. Here we show that an equation based on the processes universal to bogs explains their morphology across biomes, from Alaska, through the tropics, to New Zealand. In contrast to earlier models of bog morphology that attempted to describe only long-term equilibrium shapes4,6,7 and were, therefore, inapplicable to most bogs14-16, our approach makes no such assumption and makes it possible to infer full shapes of bogs from a sample of elevations, such as a single elevation transect. Our findings provide a foundation for quantitative inference about the morphology, hydrology and carbon storage of bogs through Earth's history, as well as a basis for planning natural climate solutions by rewetting damaged bogs around the world.

Seed settling and trapping during submerged secondary dispersal: Implications for saltmarsh recruitment and restoration

Given the decline of global salt marshes, there is a pressing need to pinpoint the key processes that limit and facilitate seed-based pioneer recruitment. Secondary seed dispersal, in the form of short-distance submerged movement, is a prerequisite for initiating pioneer establishment in adjacent tidal flats but has not been fully appreciated and understood. In this study, using a settling tube and race-track flume, seeds of four global occurring saltmarsh species were studied in terms of their settlement speed and trapping opportunity to understand how seed traits and physical settings affect submerged dispersal behavior and thus seed-based saltmarsh recruitment. Present study led to the following novel insights: 1) Seeds have density-dependent settling speeds, which are comparable to that of fine sand, but much faster than that of very fine sand and silt. Since the latter is the type of sediment commonly found in many estuaries worldwide (such as the Scheldt), seeds will typically settle faster than local sediments. A sufficiently long hydrodynamic-calm period allows slowly settling sediment to bury settled seeds, otherwise, seeds will remain uncovered if the period is short. 2) Seed trapping ratio increased linearly with surface roughness (a proxy for local topographic complexity), but this effect becomes smaller with increasing hydrodynamic intensity. Seed drag coefficient was identified as the key biotic factor contributing to interspecies variability in trapping ratio. Overall, present results suggest that submerged seed dispersal may form a primary bottleneck for salt marsh recruitment by limiting seed availability via two mechanisms: i) reduced chance of seed burial through asynchronous settling of seeds and sediment particles; ii) reduced probability of seed trapping due to encountering smooth tidal flat surfaces. This study provide mechanistic and data basis for the targeted application of biophysical models in predicting outcomes of saltmarsh recruitment and long-term maintenance, thereby informing seed-based conservation and restoration.

Blue carbon benefits from global saltmarsh restoration

Coastal saltmarshes are found globally, yet are 25%-50% reduced compared with their historical cover. Restoration is incentivised by the promise that marshes are efficient storers of 'blue' carbon, although the claim lacks substantiation across global contexts. We synthesised data from 431 studies to quantify the benefits of saltmarsh restoration to carbon accumulation and greenhouse gas uptake. The results showed global marshes store approximately 1.41-2.44 Pg carbon. Restored marshes had very low greenhouse gas (GHG) fluxes and rapid carbon accumulation, resulting in a mean net accumulation rate of 64.70 t CO2 e ha-1 year-1 . Using this estimate and potential restoration rates, we find saltmarsh regeneration could result in 12.93-207.03 Mt CO2 e accumulation per year, offsetting the equivalent of up to 0.51% global energy-related CO2 emissions-a substantial amount, considering marshes represent <1% of Earth's surface. Carbon accumulation rates and GHG fluxes varied contextually with temperature, rainfall and dominant vegetation, with the eastern coasts of the USA and Australia particular hotspots for carbon storage. While the study reveals paucity of data for some variables and continents, suggesting need for further research, the potential for saltmarsh restoration to offset carbon emissions is clear. The ability to facilitate natural carbon accumulation by saltmarshes now rests principally on the action of the management-policy community and on financial opportunities for supporting restoration.

Restoration ecology meets design-engineering: Mimicking emergent traits to restore feedback-driven ecosystems

Ecosystems shaped by habitat-modifying organisms such as reefs, vegetated coastal systems and peatlands, provide valuable ecosystem services, such as carbon storage and coastal protection. However, they are declining worldwide. Ecosystem restoration is a key tool for mitigating these losses but has proven failure-prone, because ecosystem stability often hinges on self-facilitation generated by emergent traits from habitat modifiers. Emergent traits are not expressed by the single individual, but emerge at the level of an aggregation: a minimum patch-size or density-threshold must be exceeded to generate self-facilitation. Self-facilitation has been successfully harnessed for restoration by clumping transplanted organisms, but requires large amounts of often-limiting and costly donor material. Recent advancements highlight that kickstarting self-facilitation by mimicking emergent traits can similarly increase restoration success. Here, we provide a framework for combining expertise from ecologists, engineers and industrial product designers to transition from trial-and-error to emergent trait design-based, cost-efficient approaches to support large-scale restoration.

Practical Guide to Measuring Wetland Carbon Pools and Fluxes

Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approaches for quantifying wetland C pools and fluxes. We first define each of the major C pools and fluxes and provide rationale for their importance to wetland C dynamics. For each approach, we clarify what component of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such as where and when an approach is typically used, who can conduct the measurements (expertise, training requirements), and how approaches are conducted, including considerations on equipment complexity and costs. Finally, we review key covariates and ancillary measurements that enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13157-023-01722-2.

Microbially mediated climate feedbacks from wetland ecosystems

Wetlands are crucial nodes in the carbon cycle, emitting approximately 20% of global CH4 while also sequestering 20%-30% of all soil carbon. Both greenhouse gas fluxes and carbon storage are driven by microbial communities in wetland soils. However, these key players are often overlooked or overly simplified in current global climate models. Here, we first integrate microbial metabolisms with biological, chemical, and physical processes occurring at scales from individual microbial cells to ecosystems. This conceptual scale-bridging framework guides the development of feedback loops describing how wetland-specific climate impacts (i.e., sea level rise in estuarine wetlands, droughts and floods in inland wetlands) will affect future climate trajectories. These feedback loops highlight knowledge gaps that need to be addressed to develop predictive models of future climates capturing microbial contributions. We propose a roadmap connecting environmental scientific disciplines to address these knowledge gaps and improve the representation of microbial processes in climate models. Together, this paves the way to understand how microbially mediated climate feedbacks from wetlands will impact future climate change.

Sphagnum increases soil's sequestration capacity of mineral-associated organic carbon via activating metal oxides

Sphagnum wetlands are global hotspots for carbon storage, conventionally attributed to the accumulation of decay-resistant litter. However, the buildup of mineral-associated organic carbon (MAOC) with relatively slow turnover has rarely been examined therein. Here, employing both large-scale comparisons across major terrestrial ecosystems and soil survey along Sphagnum gradients in distinct wetlands, we show that Sphagnum fosters a notable accumulation of metal-bound organic carbon (OC) via activating iron and aluminum (hydr)oxides in the soil. The unique phenolic and acidic metabolites of Sphagnum further strengthen metal-organic associations, leading to the dominance of metal-bound OC in soil MAOC. Importantly, in contrast with limited MAOC sequestration potentials elsewhere, MAOC increases linearly with soil OC accrual without signs of saturation in Sphagnum wetlands. These findings collectively demonstrate that Sphagnum acts as an efficient 'rust engineer' that largely boosts the rusty carbon sink in wetlands, potentially increasing long-term soil carbon sequestration.

Warming influences CO2 emissions from China's coastal saltmarsh wetlands more than changes in precipitation

Coastal wetlands are an important carbon sink but are sensitive to climate changes. The response of CO₂ emissions to these changes differs under different hydroclimatic conditions. Here, this article used meta-analysis to synthesize data from Chinese coastal salt marshes, to analyze sensitivities for CO₂ emissions, and then to assess the relative contributions of air temperature (T_a) and precipitation (Pre). This article used the ratio between potential evaporation (E_p) and Pre to divide Chinese coastal saltmarshes into water- (E_p/Pre > 1) and energy-limited regions (E_p/Pre ≤ 1). Results show that emissions are more sensitive to both Pre and T_a in water-limited regions (E¯ = 0.60 eV, slope = 0.37) than in energy-limited regions (E¯ = 0.23 eV, slope = 0.04). Comparing the relative effects of changes in T_a (△CO₂ = 21.86 mg m^-2 h^-1) and Pre (△CO₂ = 7.19 mg m^-2 h^-1) on CO₂ emissions shows that warming contributes more to changes in CO₂ emissions. The response of emissions to changes in Pre is asymmetric and shows that warmer and drier may have antagonistic effects, while warmer and wetter may have synergistic effects. There was a 2.15 mg m^-2 h^-1 change in emissions in energy-limited regions when Pre increased by 139.69 mm, and a decrease of -0.15 mg m^-2 h^-1 in emissions when Pre decreased by 1.28 mm in water-limited regions. Climate change has the greatest impact on Phragmites australis in CO₂ emissions, especially under warmer and wetter conditions in energy-limited regions. This indicates that warming drives CO₂ emissions, while changes in Pre (resulting in wetter or dryer conditions) can mitigate or strengthen CO₂ emissions from coastal wetlands in China. This article offers a new perspective and suggests that differences in hydroclimatic conditions should be considered when discussing carbon emissions from coastal wetlands.

An overlooked soil carbon pool in vegetated coastal ecosystems: National-scale assessment of soil organic carbon stocks in coastal shelter forests of China

Protection and restoration of vegetated coastal ecosystems provide opportunities to mitigate climate change. Coastal shelter forests as one of vegetated coastal ecosystems play vital role on sandy coasts protection, but less attention is paid on their soil organic carbon (OC) sequestration potential. Here, we provide the first national-scale assessment of the soil OC stocks, fractions, sources and accumulation rates from 48 sites of shelter forests and 74 sites of sandy beaches across 22° of latitude in China. We find that, compared with sandy beaches, shelter forest plantation achieves an average soil desalination rate of 92.0 % and reduces the soil pH by 1.3 units. The improved soil quality can facilitate OC sequestration leading to an increase of soil OC stock of 11.8 (0.60-64.2) MgC ha^-1 in shelter forests. Particulate OC (POC) is a dominant OC fraction in both sandy beaches and shelter forests, but most sites are >80 % in shelter forests. The low δ¹³C values and higher C:N ratios, which are more regulated by climate and tree species, together with high POC proportions suggest a substantial contribution of plant-derived OC. Bayesian mixing model indicates that 71.8 (33.5-91.6)% of the soil OC is derived from local plant biomass. We estimate that soil OC stocks in Chinese shelter forests are 20.5 (7.44-79.7) MgC ha^-1 and 4.53 ± 0.71 TgC in the top meter, with an accumulation rate of 45.0 (6.90 to 194.1) gC m^-2 year^-1 and 99.5 ± 44.9 GgC year^-1. According to coastal shelter forest afforestation plan, additional 1.72 ± 0.27 TgC with a rate of 37.9 ± 17.1 GgC year^-1 can be sequestrated in the future. Our findings suggest that construction of coastal shelter forests can be an effective solution to sequester more soil carbon in coastal ecosystems.

Water availability and seasonality shape elemental stoichiometry across space and time

The interaction of climate change and increasing anthropogenic water withdrawals is anticipated to alter surface water availability and the transport of carbon (C), nitrogen (N), and phosphorus (P) in river networks. But how changes to river flow will alter the balance, or stoichiometry, of these fluxes is unknown. The Lower Flint River Basin (LFRB) is part of an interstate watershed relied upon by several million people for diverse ecosystem services, including seasonal crop irrigation, municipal drinking water access, and public recreation. Recently, increased water demand compounded with intensified droughts have caused historically perennial streams in the LFRB to cease flowing, increasing ecosystem vulnerability. Our objectives were to quantify how riverine dissolved C:N:P varies spatially and seasonally and determine how monthly stoichiometric fluxes varied with overall water availability in a major tributary of LFRB. We used a long-term record (21-29 years) of solute water chemistry (dissolved organic carbon, nitrate/nitrite, ammonia, and soluble reactive phosphorus) paired with long-term stream discharge data across six sites within a single LFRB watershed. We found spatial and seasonal differences in soluble nutrient concentrations and stoichiometry attributable to groundwater connections, the presence of a major floodplain wetland, and flow conditions. Further, we showed that water availability, as indicated by the Palmer Drought Severity Index (PDSI), strongly predicted stoichiometry with generally lower C:N and C:P and higher N:P fluxes during periods of low water availability (PDSI < -4). These patterns suggest there may be long-term and significant changes to stream ecosystem function as water availability is being dramatically altered by human demand with consequential impacts on solute transport, in-stream processing, and stoichiometric ratios.

The contribution of wetland plant litter to soil carbon pool: Decomposition rates and priming effects

Plant litter input is an important driver of soil/sediment organic carbon (SOC) turnover. A large number of studies have targeted litter-derived C input tracing at a global level. However, little is known about how litter carbon (C) input via various plant tissues affects SOC accumulation and mineralization. Here, we conducted laboratory incubation to investigate the effects of leaf litter and stem litter input on SOC dynamics using the natural ¹³C isotope technique. A 122-day laboratory incubation period showed that litter input facilitated SOC accumulation. Leaf and stem litter inputs increased soil total organic carbon content by 37.6% and 15.5%, respectively. Leaf litter input had a higher contribution to SOC accumulation than stem litter input. Throughout the incubation period, the δ¹³C values of stem litter and leaf litter increased by 1.5‰ and 3.3‰, respectively, while δ¹³CO₂ derived from stem litter and δ¹³CO₂ derived from leaf litter decreased by 4.2‰ and 6.1‰, respectively, suggesting that the magnitude of δ¹³C in litter and δ¹³CO₂ shifts varied, depending on litter tissues. The cumulative CO₂-C emissions of leaf litter input treatments were 27.56%-42.47% higher than those of the stem litter input treatments, and thus leaf litter input promoted SOC mineralization more than stem litter input. Moreover, the proportion of increased CO₂-C emissions to cumulative CO₂-C emissions (57.18%-92.12%) was greater than the proportion of litter C input to total C (18.7%-36.8%), indicating that litter input could stimulate native SOC mineralization, which offsets litter-derived C in the soil. Overall, litter input caused a net increase in SOC accumulation, but it also accelerated the loss of native SOC. These findings provide a reliable basis for assessing SOC stability and net C sink capacity in wetlands.

Nutrient dynamics of 12 Sphagnum species during establishment on a rewetted bog

Peatland degradation through drainage and peat extraction have detrimental environmental and societal consequences. Rewetting is a mitigation option to restore lost ecosystem functions, such as carbon uptake, water retention, biodiversity and nutrient sequestration. Peat mosses (Sphagnum) are the most important peat-forming species in bogs. Most Sphagnum species occur in nutrient-poor habitats, however, high growth rates have been reported in artificial nutrient-rich conditions with optimal water supply. Here, we demonstrate the differences in nutrient dynamics of 12 Sphagnum species during their establishment in a one-year field experiment at a Sphagnum paludiculture area in NW Germany. The 12 species are categorized in three groups (slower, medium and fast-growing). Rapid establishment of the peat mosses is facilitated by constant and sufficient supply of nutrient-rich, low pH, and low alkalinity surface water. Our study shows that slower-growing species (S. papillosum, S. magellancium, S. fuscum, S. rubellum, S. austinii; often forming hummocks) displayed signs of nutrient imbalance. These species accumulated higher amounts of nitrogen, phosphorus, magnesium and calcium in their capitula, and had an elevated stem N:K quotient (> 3). Additionally, this group sequestered less carbon and potassium per m² than the fast and medium growing species (S. denticulatum, S. fallax, S. riparium, S. fimbriatum, S. squarrosum, S. palustre, S. centrale). Lower lawn thickness may have amplified negative effects of flooding in slower-growing species. We conclude that nutrient dynamics and carbon/nutrient sequestration rates are species-specific. For optimal outcomes of bog restoration, generating ecosystem services or choosing suitable donor material for Sphagnum paludiculture, it is crucial to consider their compatibility with existing environmental conditions.

Chlorinated organic pollutants in global flooded soil and sediments: Pollution status and potential risk

Chlorinated organic pollutants (COPs) were widely detected in anaerobic environments while there is limited understanding of their pollution status and potential environmental risks. Here, we applied meta-analysis to identify the occurrence status, pollution sources, and environmental risk of COPs from 246 peer-published literature, including 25 kinds of COPs from 977 sites. The results showed that the median concentrations of COPs were at the ng g^-1 level. By the combination of principal component analysis (PCA) and positive matrix factorization (PMF), we established 7 pollution sources for COPs. Environmental risk assessment found 73.3% of selected sites were at a security level but the rest were not, especially for the wetlands. The environmental risk of COPs was usually underestimated by the existing evaluation methods, such as without the consideration of the non-extractable residues (NER) and the multi-process coupling effect. Especially, the synergetic coupling associations between dechlorination and methanogenesis might increase the risk of methane emission that has barely been previously considered in previous risk assessment approaches. Our results expanded the knowledge for the pollution control and remediation of COPs in anaerobic environments.

Soil Carbon, Nitrogen, and Phosphorus Stoichiometry and Fractions in Blue Carbon Ecosystems: Implications for Carbon Accumulation in Allochthonous-Dominated Habitats

Blue carbon ecosystems (BCEs) including mangroves, saltmarshes, and seagrasses are highly efficient for organic carbon (OC) accumulation due to their unique ability to trap high rates of allochthonous substrates. It has been suggested that the magnitude of OC preservation is constrained by nitrogen (N) and phosphorus (P) limitation in response to climate and anthropogenic changes. However, little is known about the connection of soil OC with N-P and their forms in response to allochthonous inputs in BCEs. By analyzing soil OC, N, and P densities of BCEs from 797 sites globally, we find that, in China, where allochthonous OC provides 50-75% of total OC, soil C/P and N/P ratios are 4- to 8-fold lower than their global means, and 23%, 29%, and 20% of buried OC, N, and P are oxidation-resistant fractions that linked with minerals. We estimate that the OC stocks in China should double over the next 40 years under high allochthonous inputs and elevated N/P ratio scenarios during BCE restoration. Allochthonous-dominated BCEs thus have the capacity to enhance refractory and mineral bound organic matter accumulation. Protection and restoration of such BCEs will provide long-term mitigating benefits against sea level rise and greenhouse gas emissions.

Hidden vulnerability of US Atlantic coast to sea-level rise due to vertical land motion

The vulnerability of coastal environments to sea-level rise varies spatially, particularly due to local land subsidence. However, high-resolution observations and models of coastal subsidence are scarce, hindering an accurate vulnerability assessment. We use satellite data from 2007 to 2020 to create high-resolution map of subsidence rate at mm-level accuracy for different land covers along the ~3,500 km long US Atlantic coast. Here, we show that subsidence rate exceeding 3 mm per year affects most coastal areas, including wetlands, forests, agricultural areas, and developed regions. Coastal marshes represent the dominant land cover type along the US Atlantic coast and are particularly vulnerable to subsidence. We estimate that 58 to 100% of coastal marshes are losing elevation relative to sea level and show that previous studies substantially underestimate marsh vulnerability by not fully accounting for subsidence.

Carbon fluxes and soil carbon dynamics along a gradient of biogeomorphic succession in alpine wetlands of Tibetan Plateau

Hydrological changes under climate warming drive the biogeomorphic succession of wetlands and may trigger substantial carbon loss from the carbon-rich ecosystems. Although many studies have explored the responses of wetland carbon emissions to short-term hydrological change, it remains poorly understood how the carbon cycle evolves with hydrology-driven wetland succession. Here, we used a space-for-time approach across hydrological gradients on the Tibetan Plateau to examine the dynamics of ecosystem carbon fluxes (carbon dioxide (CO2) and methane (CH4)) and soil organic carbon pools during alpine wetland succession. We found that the succession from mesic meadow to fen changed the seasonality of both CO2 and CH4 fluxes, which was related to the shift in plant community composition, enhanced regulation of soil hydrology and increasing contribution of spring-thaw emission. The paludification caused a switch from net uptake of gaseous carbon to net release on an annual timescale but produced a large accumulation of soil organic carbon. We attempted to attribute the paradox between evidence from the carbon fluxes and pools to the lateral carbon input and the systematic changes of historical climate, given that the wetlands are spatially low-lying with strong temporal climate-carbon cycle interactions. These findings demonstrate a systematic change in the carbon cycle with succession and suggest that biogeomorphic succession and lateral carbon flows are both important for understanding the long-term dynamics of wetland carbon footprints.