As crucial blue carbon reservoirs, coastal wetlands regulate regional ecosystem functioning through vegetation succession and soil carbon (C) cycling. In tide-dominated landscapes, plant communities are arranged along geomorphology-, hydrology- and sediment-driven land-sea gradients, creating distinct habitats and soil environments. Mixed plant communities often enhance soil organic carbon (SOC), but their effects on SOC stability and C pool management in coastal wetlands remain unclear. Here, we compared SOC fractions, molecular composition, C pool indices that integrate C lability and management (CPAI, CPMI), and key environmental factors, as well as associated soil physical properties, in pure Phragmites australis wetlands, pure mangrove wetlands and mixed P. australis-mangrove communities in southeastern China. Surface (0-10 cm) soils in mixed wetlands contained 23.7 % and 6.6 % more SOC than pure P. australis and mangrove wetlands, respectively, and showed higher microbial biomass C (MBC) (+18.2 % and + 65.5 %) and dissolved organic C (DOC) (+23.8 % vs. mangroves; p < 0.05). In subsurface soils (10-30 cm), mixed wetlands reduced easily oxidizable C (EOC) by 49.5 % relative to mangroves, but increased MBC by 98.3 %, while DOC decreased by 86.5 % compared with P. australis (p < 0.05). Spectral analyses indicated higher contributions of alkoxy C and lower proportions of aliphatic, aromatic and alkyl C in mixed stands, suggesting a shift toward more microbially processed SOC. Compared with mangroves, mixed communities significantly decreased CPAI (-50.3 %) and CPMI (-45.4 %) (p < 0.05), indicating lower overall C pool activity and management efficiency despite higher labile C inputs. Mixed wetlands also exhibited higher soil water content, lower pH and reduced bulk density. Overall, plant community mixing reshaped SOC fractions, chemical composition and management indices across soil depths, highlighting its complex influence on coastal wetland C stability and sequestration trajectories under ongoing vegetation change.

Soil microorganisms drive critical ecosystem processes, including carbon (C), nitrogen (N), and phosphorus (P) cycling, yet the synergistic roles of microbial diversity, interaction networks, and life-history strategies in regulating soil multifunctionality remain unclear, particularly in hyper-arid regions. Here, we integrated taxonomic diversity, co-occurrence network complexity, and Y-A-S life-history strategies (high Yield, resource Acquisition, Stress tolerance) to explore microbial mechanisms underlying soil multifunctionality across three land-use types (desert-steppes, paddy fields, natural wetlands) in the Taklamakan Desert. Our results revealed stark contrasts: archaeal diversity was negatively correlated with soil multifunctionality, fungal diversity showed a positive correlation (P < 0.05), while bacterial diversity exhibited no significant association (P > 0.05). Archaeal and fungal network complexity negatively correlated with soil multifunctionality. Natural wetlands exhibited the highest soil multifunctionality, likely facilitated by fungal diversity and niche partitioning, whereas paddy fields showed reduced performance alongside dominance of A/S-strategists. Partial least squares path modeling further suggested that taxonomic diversity was indirectly linked to soil multifunctionality via lifehistory strategies (total effect: -0.515) and network complexity (-0.648), explaining 58.2% of variance. Overall, these findings indicate that taxonomic diversity likely contributes to soil multifunctionality through indirect paths rather than direct effects, supporting a multidimensional framework linking microbial traits to arid ecosystem functioning. These findings advance the theoretical framework for ecosystem multifunctionality and underscore that management strategies to sustain soil functionality in hyper-arid lands should account for the distinct roles of microbial taxonomic groups and their life-history strategies.

The conversion of estuarine wetlands into paddy fields has a significant impact on the global carbon (C) cycle. However, existing studies lack comparative analyses of soil fungal community succession, aggregate stability, and organic C pool stability among estuarine wetland-paddy systems distributed across different climatic zones. This study examined estuarine wetland-paddy field systems at the Yellow River Estuary (temperate), Jiulong River Estuary (subtropical), and Dongzhai Port (tropical), measuring fungal communities, soil aggregate stability, and organic C content in the 0-15 cm and 15-30 cm soil layers. The results indicate that the Ascomycota and Basidiomycota phyla dominate the fungal community. Land reclamation generally restructured the fungal community, reduced the abundance of Geomyces, and overall weakened aggregate stability, decreased the proportion of macroaggregates (>0.25 mm), and lowered soil organic C (SOC) level. Land reclamation in estuarine wetlands disrupts fungal community structure, weakens the C sequestration function of soil aggregates, reduces organic C storage capacity, and ultimately diminishes the stability of the soil C pool. This study provides a scientific basis for the conservation and restoration of wetland blue C.

Reclamation of coastal marshes into aquaculture ponds enhances methane production and emissions. However, the effects of this reclamation on methane oxidation remain unclear. This study investigated six representative coastal wetlands in eastern China, including mangroves, Suaeda salsa, and Phragmites australis systems. The effects of aquaculture pond reclamation on methane oxidation potential (MOP) and methanotrophic communities were assessed in both upper (0-15 cm) and lower (15-30 cm) sediment layers. Reclamation reduced MOP in coastal wetland sediments, with responses varying among vegetation types. In mangrove wetlands, MOP declined by 47.8% (0-15 cm) and 31.3% (15-30 cm) relative to native controls, followed by Phragmites australis wetlands (34.9% and 28.8%). In contrast, Suaeda salsa wetlands exhibited only slight reductions in MOP (9.84% and 15.8%). These declines were mainly attributed to concurrent changes in sediment properties, including bulk density, water content, pH, organic carbon, and available nitrogen. Reclamation also altered methanotrophic abundance and community composition. Specifically, the relative abundance of Methylocystis significantly decreased after reclamation, accompanied by increased methanotrophic community homogeneity. Overall, these results indicate that methane oxidation responses to reclamation vary among vegetation types and are largely mediated by vegetation-specific changes in environmental conditions and methanotrophic community structure. This study provides novel evidence of divergent methane oxidation responses to aquaculture reclamation across coastal wetlands with different vegetation types. These findings provide valuable insights into the microbial mechanisms underlying the effects of reclamation on sediment carbon cycling in coastal wetlands.

Understanding the stabilization pathways of mineral-associated organic carbon (MAOC) under plant invasion is critical for predicting soil carbon dynamics in coastal wetlands. Spartina alterniflora, a widespread invasive species, exerts substantial ecological impacts, yet its influence on MAOC stabilization remains poorly understood. This study investigated the shifts in MAOC fractions,specifically iron and aluminum oxide-associated (MAOCFe (Al)-OC), calcium-associated MAOC (MAOCCa-OC), and residual MAOC (MAOCResidual-OC), along with soil fungal communities before and after invasion at a subtropical estuarine wetland. Results show that invasion significantly increased MAOCFe(Al)-OC and MAOCCa-OC by 31% and 21%, respectively, while the chemically stable MAOCResidul-OC remained quantitatively dominant. FTIR analysis revealed an enrichment in MAOCaliphatic-OC functional groups, suggesting a shift toward more chemically diverse yet labile carbon inputs. Although fungal alpha-diversity remained unchanged, the invasion drove a distinct functional reconfiguration of the community, characterized by a transition from r-to K-strategies and the proliferation of Saprotroph. Random Forest and redundancy analyses (RDA) identified saprotrophs as pivotal biological regulators (explaining 55% of the variation), exhibiting an apparent ecological coupling with the responsive MAOCCa-OC. These findings suggest that Spartina alterniflora invasion enhances carbon sequestration not only by increasing organic inputs but also by orchestrating a Saprotroph heavy community that strengthens specific mineral-organic associations. This study highlights the synergy between fungal functional shifts and geochemical pathways as a fundamental mechanism governing blue carbon resilience under biological invasions.

Aims Mangrove re-establishment after invasive-plant control may alter soil carbon distribution and microbial nutrient acquisition, but these responses are rarely evaluated together across soil depths. We tested whether a Kandelia obovata patch re-established after Spartina alterniflora removal showed higher deep-soil organic carbon (SOC) and greater microbial allocation to phosphorus (P) acquisition than an extant S. alterniflora reference. Methods At one Minjiang Estuary site, we compared one extant S. alterniflora patch with K. obovata and Phragmites australis patches established approximately five years after S. alterniflora removal. SOC concentration, fixed-depth SOC stock, and soil and microbial C:N:P stoichiometry were measured at 0-100 cm in August 2023 and January 2024. Potential extracellular enzyme activities and ecoenzymatic vector metrics were assessed in surface soil. Results Relative to the reference, SOC concentrations in the K. obovata patch were 13.65% and 12.80% higher at 30–60 and 60–100 cm, respectively, although campaign-pooled fixed-depth SOC stock did not differ significantly. Mean potential acid phosphatase activity was 201.96% higher, and mean vector angle was greater (82.34° vs. 75.86°), indicating stronger relative allocation to P acquisition among the assayed enzymes. Total soil P did not differ significantly, whereas microbial biomass P at 60–100 cm was lower and surface microbial biomass N:P was higher in the K. obovata patch than in the reference. Conclusions These site-level findings show that post-control assessments should distinguish SOC concentration from fixed-depth stock and integrate depth-resolved carbon measurements with microbial nutrient-acquisition indicators.

Microorganisms drive anaerobic antimony (Sb) oxidation and detoxification in groundwater, how carbon source (organic vs. inorganic) regulates this process and shapes microbial adaptive strategies remains unclear. To fill this knowledge gap, microcosms were conducted with groundwater from Xikuangshan mining-area, integrating with hydrochemistry, genes quantification, and metagenomics. The results demonstrated efficient anaerobic Sb(III) oxidation coupled with NO3- reduction, regulated synergistically by Sb concentration and carbon sources. The concentration of 0.5 mM Sb(III) served as a critical threshold that triggered changes in bacterial diversity, composition, and Sb(III)-oxidation behavior. Below this, NaHCO3 promoted higher oxidation rates (P < 0.05), linked to enrichment of Hydrogenophaga, Aquabacterium, Acidovorax, and aioA genes (Sb-oxidizing gene). Above 0.7 mM Sb(III), Na-lactate activated aioA and narrowed the rate gap, accompanied by increases in both abundance and niche of Dechloromonas. In addition, elevated Sb stress reshaped the metabolic networks across microcosms. The communities prioritized energy allocation to nitrogen fixation (nifH) with multiple benefits over redundant carbon fixation (cbbL). This research expands the known range of Sb and carbon drive microbial metabolic remodeling, advancing our predictive understanding of Sb biogeochemical cycling in contaminated aquifers.

Nitrogen fertilization strongly affects methane emissions, but the dose-dependent responses of methane production and oxidation to different nitrogen forms remain insufficiently understood. Here, we incubated soils from six Chinese paddy fields under urea or (NH4)(2)SO4 at concentrations ranging from 0 to 200 mg N kg(-1) dry soil (interval: 40). Urea promoted both methane production and oxidation potentials, with stronger enhancement for production at <170 mg N kg(-1), and oxidation within 170-200 mg N kg(-1). This aligns with field observations where urea initially increases and then reduces methane emissions as fertilization rates rise from Chinese paddy fields. In contrast, (NH4)(2)SO4 addition suppressed both processes, with stronger inhibition for oxidation at <140 mg N kg(-1), and production at 140-200 mg N kg(-1), suggesting (NH4)(2)SO4 is more effective than urea in reducing methane emissions. Moreover, CH4 production potentials under (NH4)(2)SO4 addition exhibited different patterns between fields with different nitrogen fertilization histories. In fields with high nitrogen inputs-characterized by higher soil carbon and nitrogen contents, lower relative abundance of Methanothrix, and higher abundance of Methanosarcinaceae-CH4 production was initially stimulated but subsequently inhibited as (NH4)(2)SO4 concentrations increased. In contrast, CH4 production in low nitrogen input fields was consistently inhibited across the entire (NH4)(2)SO4 gradient. Overall, this study highlighted the distinct dose-response patterns of methane production and oxidation to urea or (NH4)(2)SO4 in Chinese paddy fields with varying nitrogen fertilization rates, providing insights for optimizing nitrogen management strategies to mitigate methane emissions.

Removing invasive Spartina alterniflora from estuarine wetlands does not guarantee synchronous recovery of soil carbon (C) pools; recovery depends on the replacement species, nutrient supply, and microbial metabolism. We investigated subtropical estuarine wetlands in China comprising S. alterniflora, Phragmites australis–re-established, and Kandelia obovata–re-established wetlands, measuring soil organic C (SOC) content and stock, soil–microbial C:N:P stoichiometry, extracellular enzyme activities, and microbial C use efficiency (CUE) across 0–100 cm profiles in growing and non-growing seasons. P. australis replacement reduced SOC stocks by 29.48% (0-30 cm) and 27.58% (60-100 cm) (p < 0.05). K. obovata replacement increased SOC content by 13.65% (30-60 cm) and 11.35% (60-100 cm) (p < 0.05), yet SOC stocks remained lower than in S. alterniflora wetlands, a decoupling attributable to incomplete recovery of soil bulk density. Microbial biomass, stoichiometry, and enzyme activities responded more sensitively than total soil nutrients to replacement pathways. K. obovata replacement significantly elevated acid phosphatase, cellobiohydrolase, and N-acetylglucosaminidase activities, coinciding with lower CUE and stronger phosphorus (P) limitation. These results demonstrate that post-control SOC recovery is pathway-dependent and non-linear: K. obovata replacement more effectively promotes SOC accumulation and biogeochemical functioning than P. australis replacement, although full stock recovery requires longer-term rehabilitation of soil structure and phosphorus availability.

Sequestrating soil organic carbon (SOC) in paddy ecosystems is vital for enhancing soil quality and mitigating climate change. Ratoon rice (RR) offers the advantage of being planted once and harvested twice, while also reducing damage to soil structure compared to the intensive tillage practices in double-cropping rice (DR) systems. Despite its potential for SOC accumulation, the underlying stabilization mechanisms remain poorly understood. Through a field comparative study of RR with DR, we systematically investigated the dynamics of SOC fractions, aggregate stability, Fe/Al-bonded organic carbon (Fe (Al)-SOC), and bacterial communities. Our findings demonstrate that RR significantly increased SOC stocks by 10.73%–31.55% compared to DR, while also boosting subsoil readily oxidizable carbon (ROC) reserves. Mechanistically, compared with the DR system, the RR system markedly increased the proportion of macroaggregates in subsoil as well as their contribution to aggregate-associated organic carbon. In addition, RR enhanced aggregate stability MWD (Mean Weight Diameter) and GMD (Geometric Mean Diameter) during the first harvest and fallow period. Moreover, RR promoted the formation of Fe (Al)-SOC, thereby enhancing chemical carbon stabilization. The shift to RR also optimized bacterial community structures and upregulated carbon-cycling metabolic functions. PLS-SEM analysis further revealed that RR reversed the negative regulatory effect of aggregates on SOC sequestration found in DR. By fostering a synergistic coupling among aggregates, microorganisms, and Fe/Al oxides, RR significantly enhances the carbon sequestration capacity of paddy soils.

Global sea level is projected to rise 0.28-1.02 m by 2100, exacerbating flooding and saltwater intrusion in estuarine wetlands. This threatens to alter soil iron (Fe) and organic carbon (C) pools, potentially affecting Fe-bound organic C (Fe-OC) formation. Given that Fe-OC represents a critically stable carbon reservoir-often referred to as the “rusty carbon sink”-its preservation is essential for the long-term carbon sequestration function of estuarine wetlands. Therefore, understanding how sea level rise influences Fe-OC dynamics is crucial for predicting future changes in coastal wetland carbon sink capacity. However, how enhanced flooding and salinity regulate Fe-OC via Fe/C pools and microbial processes remains unclear. We conducted a one-year in-situ experiment in a Phragmites australis wetland (Min River Estuary) with control (CK, natural tidal flooding) and two treatments receiving additional tidal water (TW) and saline water (SW) besides natural tidal flooding. Results showed that: (1) TW and SW increased soil free Fe oxide (Fed) by 70.7±5.6% and 94.8±8.3% (p < 0.05), while soil organic C remained unchanged (p > 0.05), indicating that the soil Fe pool is more responsive to sea level rise (enhanced flooding and salinity) than the soil organic C pool. (2) Soil Fe-OC content increased by 10% (TW) and 20% (SW), with its contribution to organic C rising by 5.3% and 9.2%. Concurrently, soil CO2 emission fluxes decreased significantly under both treatments and correlated negatively with Fe-OC content. Aggregated boosted tree (ABT) analysis confirmed Fed as the key driver of Fe-OC formation. (3) The diversity and abundance of the soil C-fixing microbial community (cbbL) remained unchanged (p > 0.05), but Fe-oxidizing bacteria (FeOB) and Fe-reducing bacteria (FeRB) increased with flooding-salinity (p < 0.05), especially FeRB. This microbial shift did not immediately alter soil Fe(II) or Fe(III), implying compensatory processes (e.g., root oxygen release). Mantel analysis revealed stronger FeOB/FeRB-Fe pool correlations than cbbL-C pool links. (4) Path analysis revealed that sea-level rise regulates FeOB/FeRB community structure to drive Fe redox cycling, transforming Fe minerals and dominating Fe-OC formation. This study reveals a “mineral-microorganism” synergistic mechanism underlying Fe-OC sequestration under sea-level rise: the coupled activities of FeRB (reductive dissolution) and FeOB (oxidative precipitation) drive Fe redox cycling, endowing estuarine wetland C pools with resilience to environmental stress. These findings offer new insights for coastal blue carbon management, suggesting that regulating Fe cycles could optimize Fe-OC stability and improve coastal C sink adaptability.

In desert ecosystems, deep-rooted plants like Alhagi sparsifolia contribute not only to wind prevention and sand fixation but also to the transport of carbon into deep soil layers through their root systems. However, the sources and stabilization mechanisms of soil organic carbon (SOC) following plant carbon input remain unclear. This study investigated a dominant A. sparsifolia community at the southern edge of the Taklimakan Desert. We analyzed plant traits and the vertical distribution (0-200 cm) of SOC fractions-particulate organic carbon (POC), mineral-associated organic carbon (MAOC), and calcium/iron-bound organic carbon (Ca/Fe-OC)-along with carbon sources (microbial biomass, microbial necromass, and plant residue). As growth advanced, stem and root biomass increased, while leaf and thorn biomass remained stable. SOC and POC decreased by 5.38-29.43% with soil depth, whereas MAOC and Ca/Fe-OC increased by 32.34-48.15%. Plant residue contributed more to SOC (average 30.56%) than microbial necromass (8.28%), and both contributions increased by 9.60-167.68% with soil depth. No significant correlation was found between plant residue and SOC fractions, but a significant correlation with microbial necromass. In conclusion, although plant residues constitute the primary source of SOC in desert ecosystems, microbial necromassa exerts a stronger influence on SOC stability.

Functional microorganisms play key roles in sustainable agriculture, and seedling technologies leveraging the priority effect are vital for unlocking the potential of these microorganisms. However, there is still a lack of systematic assessments of microbial seedling technologies on yield and soil properties under field conditions. This study employed mycorrhizal and bio-organic seedling cultivation (MSC and BOSC) to explore the effects of arbuscular mycorrhizal (AM) fungi, mineral fertilizers, organic fertilizers, and other plant-beneficial microbes (PBMs) on maize yield and soil properties in the field. The results showed that AM fungi significantly increased maize yield by mediating phosphorus nutrition and improved agronomic traits such as ear length, ear diameter, and grain number per ear. However, AM fungi had no significant effect on soil properties, including pH, electrical conductivity, total nitrogen, soil organic carbon, fungal diversity, and bacterial diversity. Inoculation with PBMs (excluding AM fungi) at the seedling stage might not maintain the rhizosphere niche in the field, and therefore did not effectively promote maize growth. In addition, adding mineral and organic fertilizers to the seedling medium made the seedlings stronger, but had a limited effect on the yield. For economic reasons, we recommend that mycorrhizal seedling cultivation without addition of fertilizers. Our research provides important implications for the use of functional microorganisms in agriculture.

Soil organic carbon (SOC) dynamics in hyper-arid ecosystems are governed by allocation shifts between plantand microbial-derived carbon (C). However, the underlying mechanisms governing these dynamics under landuse change remain poorly quantified. To address this, lignin phenols, amino sugar biomarkers, and microbial functional trait analysis were integrated to evaluate how microbial life-history strategies and environmental stressors regulate SOC accumulation across three ecosystem types (natural wetlands, paddies, and desert-steppes) in oasis-desert ecotones of the Taklamakan Desert. Natural wetlands exhibited the highest SOC (4.15 g kg-1) content, with 19.9 % derived from microbial necromass-primarily fungal component-due to alleviated nitrogen limitation [higher nitrogen/phosphorus (N/P) ratio: 0.928] and dominance of microbial growth-yield (Y) strategies. In contrast, paddies (SOC content: 2.57 g kg-1) exhibited the highest plant-derived C contribution (28.7 % of SOC), where plant-derived C was negatively correlated with SOC content, likely driven by C limitation and priming effects under reduced microbial Y-strategist abundance. Desert-steppes (SOC content: 3.44 g kg-1) showed minimal microbial necromass accumulation (6.1 % of SOC) and advanced lignin oxidation (elevated syringyl/vanillyl and cinnamyl/vanillyl), reflecting drought-induced depletion of Y-strategists and incomplete decomposition. Soil salinity was observed to suppress microbial necromass input, while N-P stoichiometry and available N facilitated its accrual. Collectively, our findings indicate a stability dichotomy: wetlands sustain persistent SOC through microbial necromass enrichment, whereas agricultural conversion shifts SOC toward plant-derived C prone to destabilization. Strategies for SOC conservation in hyper-arid oasis-desert ecotones should prioritize the preservation of natural wetlands coupled with implementation of balanced N-P fertilization in anthropogenically managed ecosystems (e.g., paddies). This integrated approach enhances microbial contributions to SOC resilience under ongoing land-use changes.

Afforestation in arid regions is a widely promoted strategy for enhancing soil organic carbon (SOC) storage and mitigating climate change. However, how the trade-offs among Y-A-S strategies dictate the non-linear trajectory of SOC accumulation over decades in hyper-arid ecosystems remains poorly understood. Here, SOC dynamics and microbial regulatory processes were examined across a chronosequence of poplar plantations (7, 12, and 22 years) at two soil depths (0-30 cm and 30-60 cm) along the periphery of the Taklimakan Desert. SOC accumulation exhibited a non-linear trajectory: rapid increases occurred during early to mid afforestation (7-12 years), with SOC rising by 41.6-70.5% in topsoil and 23.9-52.3% in subsoil, followed by pronounced slowing and stabilization from 12 to 22 years, particularly in deeper layers. These patterns were closely associated with shifts in microbial life-history strategies. Afforestation improved soil conditions, including increased total nitrogen and reduced pH and electrical conductivity, driving a coordinated microbial reorganization characterized by enhanced growth-yield (Y) and resource-acquisition (A) strategies and a decline in stress-tolerant (S) strategies. This coupled shift in soil resources and microbial strategies fostered sustained SOC accumulation. Notably, the abundance of key Y-A-S taxa strategies peaked around 12 years, suggesting a critical ecological turning point toward stabilization of the soil and microbial community. This finding indicates that targeted nutrient management during this pivotal stage may optimize carbon sequestration in arid afforestation systems. Overall, this study underscores the importance of integrating microbial life-history strategies into managing belowground carbon dynamics in arid ecosystems.

Soil microbes represent an important driving force of biogeochemical cycles and are closely related to the soil carbon (C) cycle during afforestation process. Despite their ecological significance, the paucity characterized the mechanistic role of soil microbial C-cycling processes (MCCPs) in hyper-arid regionslimits our ability to assess soil organic carbon (SOC) dynamics and terrestrial C feedbacks to climate change. The present study integrates metagenomics to quantitatively evaluate the MCCPs dynamics across soil profiles (topsoil vs subsoil) in both uncultivated land (0 Y) and Populus alba var. pyramidalis Bunge shelterbelts of different afforestation years (7-, 12-, 22-years-old) along the Taklimakan Desert periphery. Results showed that C fixation was the predominant MCCPs, influenced by afforestation years and soil depth. Shelterbelt establishment significantly increased the concentration of SOC (+57.57 %), the relative abundance of microbial C fixation process (+16.35 %) and methanogenic process (+11.00 %) across both soil layers compared to 0Y, while exhibiting depth-dependent C decomposition patterns (topsoil +12.83 % vs subsoil-8.92 %). Microbial communities demonstrated increased Simpson diversity in topsoil but maintained subsoil stability post-afforestation. Interestingly, network analysis revealed an intensification of positive edges in C fixation process (+127.44 %) and a reduction in negative edges in C decomposition process (-28.47 %). Energy optimization strategies emerged, with microbial communities preferentially utilizing low-energy C fixation pathways under nutrient-deficient conditions. Crucially, afforestation-induced modifications in key edaphic parameters (soil nutrient condition (-49.96 %) and electrical conductivity (-74.42 %)) were identified as primary drivers of MCCPs enhancement and subsequent SOC accumulation. However, despite sustained SOC accumulation in late afforestation stages (22-year period), the marked EC elevation underscores the critical need to integrate secondary salinization control into plantation management frameworks. This study establishes MCCPs as pivotal biological mediators of C sink formation during ecological restoration. We recommend that future afforestation projects in hyper-arid regions simultaneously enhance microbial C fixation pathways and soil nutrient availability to maximize C sequestration.

Subsurface karst systems represent substantial but underexplored methane sinks, yet the identities and activities of cave-dwelling methanotrophs remain poorly characterized. We detected increased methane oxidation rates from 2.9 ± 0.1 to 90.7 ± 4.5 ng·g-1·hour-1 while supplied with 2 to 500 parts per million (ppm) CH4 to cave sediments. Atmospheric methanotroph Upland Soil Clusters γ (USCγ), responsible for this oxidation, was further assigned to three genera within the family Candidatus (Ca.) Methyloligotrophaceae, including two previously unrecognized genera. Nano-scale secondary ion mass spectrometry (NanoSIMS) imaging and the produced 13C-PLFAs (phospholipid fatty acids) and 13CO2 in 13CH4-fed microcosm confirmed methane as both carbon and energy sources. These methanotrophs exhibited low half-saturation constant (Km; 138.8 ± 15.8 ppm), high carbon assimilation efficiency (>50%), and metabolic versatility, as revealed by metagenomics and metatranscriptomics analyses. By extrapolating global distribution of Ca. Methyloligotrophaceae and comparing methane oxidation rates between caves and soil ecosystems, we conservatively estimate that subsurface karst in southwest China sequester ~0.56 Tg CH4 annually. These findings highlight the ecological importance of karst ecosystems as a previously overlooked methane sink.

Coastal wetlands are important blue carbon ecosystems, yet increasing nitrogen (N) inputs may threaten soil organic carbon (SOC) persistence. Silicon (Si), a key element linking terrestrial and marine biogeochemical cycles, may buffer SOC persistence under N loading, but the underlying mechanisms remain unclear. We conducted an in situ N and Si addition experiment in a subtropical estuarine Phragmites australis wetland in southeastern China, with four treatments: control (CK), N addition (N), Si addition (Si), and combined N and Si addition (N+Si). SOC persistence mechanisms were assessed through aggregate-mediated physical protection, mineral-associated chemical protection, and carbon-fixing bacterial communities. Across the 0–60 cm soil profile, N, Si, and N+Si additions did not significantly change SOC content or stock compared with CK. However, both variables tended to decrease under N addition. N addition weakened physical protection by reducing mean weight diameter (MWD), geometric mean diameter (GMD), and the proportion of >0.25 mm water-stable aggregates (DR0.25), while shifting SOC retention toward finer particle-size fractions. N addition also reduced mineral-associated organic carbon (MAOC) and Fe(Al)-bound SOC. Compared with CK, MAOC in the 20–40 cm layer decreased by 11.55%, and Fe(Al)-SOC decreased by 10.78%–13.24% across the 0–60 cm profile. In contrast, N+Si maintained higher MAOC and Fe(Al)-SOC levels than N addition alone, indicating that Si addition alleviated the N-induced weakening of mineral-associated carbon protection. Carbon-fixing bacterial communities responded mainly through shifts in OTU composition and dominant genera; N addition had fewer unique OTUs (702) than CK (869), whereas α-diversity showed no significant change and was weakly associated with SOC content and stock. Overall, enhanced N loading may compromise SOC persistence before detectable changes occur in total SOC pools, whereas Si addition can partially buffer the vulnerability of blue carbon persistence by maintaining aggregate stability and promoting MAOC formation.

Coastal-estuarine wetlands store organic carbon (OC) far in excess of their area, in part because tidal redox oscillations sustain reactive iron phases that bind OC. Aquaculture conversion is the dominant disturbance to these wetlands in China, yet whether it alters the magnitude of iron-bound OC (Fe-OC) or the mechanism by which iron stabilizes OC has remained unresolved. Here we show that conversion does both, and that the mechanistic shift is the more consequential change. Across ten paired natural wetlands and aquaculture ponds spanning tropical to temperate China and three vegetation types (Suaeda salsa, Phragmites australis, mangrove), reclamation lowered soil Fe-OC by 32 to 51% and depleted reactive solid-phase Fe pools (Fed, Feo, Fep). The Fe(III)/Fe(II) ratio declined by 9 to 54%, the molar OC/Fe ratio of Fe-OC fell from above 1 to below 1, and the C/N ratio dropped by 11 to 66%, indicating less OC stabilized per unit reactive Fe. Fourier-transform infrared spectroscopy (FTIR) showed a consistent decline in the aromatic-to-alkoxyl C ratio, evidence that the remaining Fe-OC is structurally less stable. Random-forest and structural-equation analyses revealed a regime shift in the controls on Fe-OC: carbon-supply variables governed Fe-OC in natural wetlands, whereas iron-reactivity variables took over in ponds, and the model explained 68% of Fe-OC variance. These changes were directionally consistent across vegetation types despite divergent pathways, pointing to a cross-system vulnerability of the iron-mediated carbon sink to tidal disconnection. Our study provides process-based evidence that aquaculture-pond retirement and wetland restoration should rebuild tidal connectivity and reactive-iron regeneration, rather than targeting soil-carbon stocks alone.