Despite the widespread use of Tillandsia usneoides as a biomonitor for atmospheric Hg-0 pollution, little is known about its dose-dependent physiological and molecular responses to Hg-0 exposure. Here, we integrated twenty physiological biomarkers, across five categories with transcriptomic and metabolomic analyses, to reveal the potential roles of metal-chelation partitioning, hormetic trade-offs, energy metabolism regulation, and membrane lipid remodeling in Hg-0 tolerance. We first identified O-2(& centerdot;-) and H2O2 as sensitive damage indicators, and CAT, POD, APX, MDHAR, and MT as sensitive response indicators. Among them, CAT and POD showed the most robust resistance across a wide concentration range. We further uncovered a trade-off-mediated hormesis pattern, where a low Hg-0 dose (5 ng & centerdot;m(-3)) enhances antioxidant and chelation defenses without evident costs. At concentrations <= 10 ng & centerdot;m(-3), Hg binding was consistently governed by MT-mediated sequestration (up to 1035-fold induction). The 10 ng & centerdot;m(-3) concentration represents a threshold at which stimulation and inhibition coexist likely due to metabolic resource reallocation. In contrast, higher doses (50-500 ng & centerdot;m(-3)) induced excessive ROS production, collapse of cellular redox balance, and membrane lipid peroxidation, marking transition from adaptation to injury. Multi-omics evidence also revealed dose-segmented regulatory strategies. At concentrations <= 50 ng & centerdot;m(-3), elevated terpenoid levels were observed, which may be associated with ROS detoxification. Conversely, exposure to 50-500 ng & centerdot;m(-3) Hg-0 triggered a shift toward PC-dominated chelation (285-307 fold increase) and suppression of photosynthetic carbon assimilation. It also activated MAPK cascades, phenylpropanoid biosynthesis, and cytoskeletal remodeling. In addition, ABC transporters mediated the transport of metal-thiol complexes collectively, potentially related to detoxification and structural defense. Overall, this study identifies a concentration-sensitive regulatory window governing redox balance, energy metabolism, and Hg chelation. This framework provides a new insight into potential mechanisms of Hg-0 detoxification.

Organic amendments in paddy fields, although agronomically beneficial, can potentially stimulate mercury (Hg) methylation due to distinct shifts in soil properties triggered by different types of amendments. Identifying the specific conditions that lead to heightened Hg methylation is thus essential for risk mitigation and sustainable management. Through incubation experiments with rice straw (RS), pig manure (PM), cow dung (CD) and chicken manure (CM), key drivers of Hg methylation were identified by linking methylation extent to amendment-induced dynamics in soil pH, Eh, Fe/S, and organic matter. Results revealed amendment-specific temporal dynamics governed by organic matter composition and reactivity. Rice straw and PM triggered a rapid Eh decline to -300 mV, concurrently accelerating Fe/S reduction and causing early methylmercury (MeHg) peaks on day 10 (7.51 ± 1.16 ng/g) and 18 (3.94 ± 0.32 ng/g), respectively. In contrast, CD and CM exhibited delayed Eh minimization and MeHg peaks (1.75 ± 0.58 and 12.94 ± 0.88 ng/g, respectively) until day 70. This differential MeHg production pattern was mainly driven by Eh-induced Fe/S reduction, which enhanced Hg bioavailability through reductive iron-oxides dissolution and subsequent soluble Hg-S complexes formation, as well as increased abundance of Hg-methylating microbes. These findings highlight that organic materials decomposition kinetics regulate MeHg formation via reductive Fe-S cycling, supporting targeted contamination mitigation strategies in agriculture.

The Tibetan Plateau stores mercury (Hg) pollutants in its glaciers, which can be methylated by microorganisms into more neurotoxic methylmercury (MeHg) under climate warming, posing a significant threat to downstream ecosystems. However, microbial Hg methylation in glaciers across different climate zones on the plateau is poorly understood. To investigate the influence of climate zones on Hg methylation, we selected the Kuqionggangri Glacier (monsoon zone) and Tianshan Glacier No. 1 (westerly zone) for a comparative study. By measuring total mercury (THg) and MeHg concentrations, along with physicochemical parameters, in snow and ice, and by combining these measurements with high-throughput 16S rRNA sequencing, we explored the underlying mechanisms. The results show that although the THg concentration in the westerly-zone glacier (66.2 ng/L) was significantly higher than in the monsoon-zone glacier (24.3 ng/L), the MeHg/THg ratio was markedly lower (0.11% vs. 0.23%). This spatial differentiation is primarily governed by climate-zone-dominated material transport patterns: monsoon-transported, abundant organic matter (total organic carbon, 3.86 mg/L) promoted the development of Hg-methylating microorganisms (such as Nitrospira and Desulfovibrio), whose relative abundance (3.8%) was much higher than in the westerly zone (0.15%). Co-occurrence network analysis further corroborated the pivotal role of these key taxa in the microbial interaction network. This study systematically reveals the spatial heterogeneity of microbial Hg methylation across glaciers of the Tibetan Plateau, thereby providing a scientific basis for assessing the biogeochemical cycling and ecological risks of Hg in glacial ablation zones.

Long-term observations of atmospheric mercury concentrations and statistical methods based on observations are important tools for quantifying the impacts of anthropogenic and natural disturbances on the global atmospheric mercury pool. Jiuzhaigou is located in the transitional zone between the Qinghai-Tibet Plateau and the Sichuan Basin, at an altitude of 2000-3500 m in the subalpine zone. Investigating the dynamics of atmospheric mercury in Jiuzhaigou can provide a basis for in-depth analysis of mercury transport characteristics on the Qinghai-Tibet Plateau and global cycling processes. In this study, continuous monitoring of gaseous elemental mercury (GEM) in Jiuzhaigou was conducted for two years from 2021 to 2023 using a high time-resolution automatic mercury analyzer. The results showed that the average concentration of GEM in Jiuzhaigou was 1.25 +/- 0.41 ng/m3, at the global background concentration of atmospheric mercury. However, the GEM concentration in Jiuzhaigou exhibited significant temporal variations, with higher concentrations in winter and lower concentrations in summer, and a daily variation pattern of higher concentrations at night and lower concentrations during the day. The effects of meteorological factors on GEM concentration were quantified using Generalized Additive Models (GAMs), indicating that relative humidity had a significant impact on GEM, and the inter-annual differences in GEM may also be influenced by atmospheric pressure and wind speed. The Potential Source Contribution Function (PSCF) model based on backward trajectories analyzed the variations of potential source areas of GEM in the atmosphere in Jiuzhaigou during spring and winter, while local air masses near the boundary layer height dominated the input in summer and autumn.

The Tibetan Plateau stores mercury (Hg) pollutants in its glaciers, which can be methylated by microorganisms into more neurotoxic methylmercury (MeHg) under climate warming, posing a significant threat to downstream ecosystems. However, microbial Hg methylation in glaciers across different climate zones on the plateau is poorly understood. To investigate the influence of climate zones on Hg methylation, we selected the Kuqionggangri Glacier (monsoon zone) and Tianshan Glacier No. 1 (westerly zone) for a comparative study. By measuring total mercury (THg) and MeHg concentrations, along with physicochemical parameters, in snow and ice, and by combining these measurements with high-throughput 16S rRNA sequencing, we explored the underlying mechanisms. The results show that although the THg concentration in the westerly-zone glacier (66.2 ng/L) was significantly higher than in the monsoon-zone glacier (24.3 ng/L), the MeHg/THg ratio was markedly lower (0.11% vs. 0.23%). This spatial differentiation is primarily governed by climate-zone-dominated material transport patterns: monsoon-transported, abundant organic matter (total organic carbon, 3.86 mg/L) promoted the development of potential Hg-methylating microorganisms (such as Nitrospira and Desulfovibrio), whose relative abundance (3.8%) was much higher than in the westerly zone (0.15%). Co-occurrence network analysis further corroborated the pivotal role of these key taxa in the microbial interaction network. This study systematically reveals the spatial heterogeneity of microbial Hg methylation across glaciers of the Tibetan Plateau, thereby providing a scientific basis for assessing the biogeochemical cycling and ecological risks of Hg in glacial ablation zones.

Soil organic matter (SOM) dynamics driven by cropland management are critical for carbon sequestration in agricultural ecosystems. The stability of SOM in paddy soils under different management regimes has been widely studied, yet the mechanisms by which winter-fallow practices regulate SOM, while simultaneously accounting for microbial processes, carbon composition, and mineral protection, remain insufficiently understood. This study examined the effects of fully flooded (FF), flooded-to-moist (FM), and fully drained (FD) management on SOM stability in paddy soils during the fallow period by assessing SOM composition, carbon sources, microbial community dynamics, and SOM mineralization with a particular focus on temperature sensitivity (Q10). Soil organic carbon (SOC) contents were significantly higher under FF and FM than under FD. However, FF primarily promoted the accumulation of labile carbon fractions, including particulate organic matter (POM), while the absence of strong mineral protection leads to higher Q10 values, indicating that SOM in these soils is more vulnerable to warming. In contrast, FM increased microbial diversity and promoted the formation of mineral-associated organic matter (MAOM), thereby stabilizing SOM and facilitating the accumulation of more stable carbon pools. Soils under FM and FD, with higher MAOM, exhibited significantly lower Q10 values compared with FF, underscoring the role of MAOM in buffering carbon loss under elevated temperatures. Overall, FM emerged as a more sustainable and resilient management strategy for maintaining SOM stability in paddy soils. These results emphasize the need to account for multiple interacting processes in land management strategies to improve SOM stability and promote long-term carbon storage under changing climatic conditions.

Monitored seabird populations have declined by up to 70% worldwide since the 1950s. Yet, data on long-term seabird population dynamics prior to the anthropogenic era are largely unknown. This limits our ability to understand future population trajectories, particularly in the Southern Ocean, where seabirds are facing multiple environmental threats. Here, we use mercury (Hg) derived from seabird guano in peatland catchments as a tracer of colony population sizes on sub-Antarctic Bird Island (South Georgia). Peat Hg flux and isotope signature results show that the first sustained seabird colonies after deglaciation were established on the island between 6800 and 6100 years ago, predating evidence for colonization on other sub-Antarctic islands by more than 1,000 y. The four subsequent periods with large local seabird populations occurred during phases of less intense Southern Hemisphere westerly winds. Our study unveils significant and repeated millennial-scale shifts in seabird abundance in response to natural climate changes, implying that the present-day increase in westerly wind intensity may lead to further declines in seabird populations in the Southern Ocean.

Soil dissolved organic matter (DOM) bio-stability is critical for understanding carbon (C) cycling and ecosystem functioning. Existing approaches for estimating DOM biodegradability are constrained by the need to balance accuracy, scalability, and cost-effectiveness, given DOM’s chemical complexity and methodological limitations. Soil DOM is widely used as a proxy for soil organic matter (SOM) persistence, yet direct empirical validation remains scarce. Here, we applied an integrative index, the persistence index (PI), calculated using ecosystem multifunctionality frameworks based on multiple properties, including diverse optical properties, to evaluate DOM persistence. Soil DOM samples from forest, grassland, and cropland soils were subjected to 14-day biodegradation incubation experiments, and degradation kinetics were modeled using a double-exponential function to quantify labile and stable fractions. Biodegradability was ecosystem-specific, with forest soil DOM exhibiting the lowest degradability and the longest mean residence time (MRT), followed by grassland and cropland. PI values correlated strongly with biodegradation parameters: negatively with labile DOM and positively with stable fractions and MRT. Optical-derived PI mirrored these trends, confirming its promise as a rapid, cost-effective proxy for DOM stability. Furthermore, DOM biodegradability also showed significant correlations with SOM persistence metrics, highlighting the coupling between the solid and aqueous phases of SOM. These ecosystem-specific differences in DOM stability have direct implications for land-use management, integrated watershed stewardship, and climate mitigation strategies. This study highlights PI’s robustness as a potential framework for cross-ecosystem comparisons, supporting methodological reference in environmental management, C sequestration, and contaminant risk reduction across diverse ecosystems.

Water level fluctuation zones (WLFZs) are recognized as hotspots for methylmercury (MeHg) production. In these areas, the total culturable aerobes in soils are significantly positively correlated with MeHg production, suggesting a role of facultative bacteria in the generation of MeHg; however, the biotransformation pathways involved remain unclear. In this study, the facultative Raoultella terrigena TGRB3 strain, isolated from WLFZ soils of the Three Gorges Reservoir, was used to investigate Hg(II) conversion in 3-(N-morpholino) propane sulfonate incubation buffer under hypoxic or oxic conditions. This facultative bacterium exhibited different Hg(II) bioconversion pathways based on the oxygenation state, with Hg(II) primarily converted to MeHg under hypoxic conditions and to elemental Hg (Hg0) under oxic conditions. These findings confirm that oxygen content is a critical environmental factor that can alter Hg(II) metabolic pathways through biological stress responses in facultative bacteria. The results enhance our understanding of how bacteria lacking hgcAB contribute to MeHg production by elucidating the mechanisms underlying Hg bioconversion, and also provide basic information for further evaluating the risk associated with soil MeHg under alternating hypoxic-oxic conditions, such as those in WLFZs.

Benthic bioturbation exerts species-specific control over heavy metals mobilization in sediments, though mechanistic drivers remain poor understood. Using sediment-water microcosms colonized by three functionally distinct benthos (Limnodrilus hoffmeisteri (LH), Cipangopaludina cahayensis (CC), Corbicula fluminea (CF)), this study explored the metal distribution in overlying water. Release flux, cumulative release, and kinetic modeling elucidated mobilization mechanisms, while benthos-sediment accumulation factors (BSAFs) quantified bioaccumulation. The concentrations of target heavy metals were determined using inductively coupled plasma-mass spectrometry (Cu, Cr, As, Zn, Ni), DMA-80 direct Hg analyzer (sediments and benthos Hg), and two-step gold amalgam-cold atomic fluorescence spectrometry (water Hg). The results indicated that: (1) Short-term disturbances enhanced all the heavy metal release by LH, which reduced release of Cr and As by CC and of Cr by CF. (2) Heavy metals release by LH was mainly in particulate form (p < 0.05), while CC and CF predominantly released dissolved Cu and As. (3) Initial release intensities were species-specific and metal-dependent. LH displayed higher Hg and Zn but lower Cu, As, and Cr release than CC and CF (p < 0.05). (4) Kinetic analyses indicated pore diffusion dominated for LH, versus chemisorption for CC and CF. (5) CF bioaccumulated Hg, Zn, and As (BSAFs=0.94, 0.43 and 0.27) at 2.4-fold higher levels than CC, while CC retained more Cu (BSAFs=0.67). These species-dependent mechanisms provided a scientific basis for lake management strategies targeting benthic-mediated contaminant flux, particularly LH-driven Cu, Ni, and Zn and CF-mediated As mobilization.

Long-term stockpiling and weathering of coal gangue (CG) leads to heavy metals contamination in surrounding soils, posing substantial ecological risks. Identifying the pollution characteristics and sources of these HMs is therefore essential for developing targeted regional pollution control strategies. This study conducted a comprehensive source-oriented assessment to prioritize control heavy metals in soils around a CG dump in Southwestern China, integrating concentration analysis, ecological risk evaluation, and multi-model source apportionment. Results revealed that Cd was the most significant contaminant, with a median concentration of 2.4 mg/kg. Approximately 40% of sampling sites exceeded the risk intervention value for Cd in agricultural soil, indicating severe Cd contamination. Over half of the sampling sites exhibited a very high ecological risk, primarily driven by Cd and Hg. Source apportionment based on the APCS-MLR and PMF models identified four principal sources: parent material, industrial activities, a composite source associated with CG storage and historical coal transportation, and agricultural practices. An integrated analysis of interactions within the soil-source-risk system identified Cd associated with CG storage and historical coal transportation as the priority control factor for potential ecological risk. This research applies an integrated, risk-prioritized and source-oriented framework for tracing heavy metals, providing scientific supports for targeted contamination control of soils affected by historical CG storage.

Immobilizing bioavailable mercury in paddy soils suppresses methylation and prevents rice accumulation. Conventional remediation fails to address ultra-trace bioavailable Hg in porewater (typically <100 ng L-1) amid dissolved organic matter and ionic interference. Here, we report a nitrogen-enriched activated carbon functionalized with in situ-grafted porous graphitic carbon nitride for mercury immobilization. This material features facile synthesis, high surface area, abundant active sites, and exceptional stability. Density functional theory calculations reveal that amine-heptazine sites achieve Hg binding energies of-89.47 to-95.01 kcal mol(-1)-fourfold stronger than thiol-Hg bonds (-22.37 kcal mol(-1)). The engineered carbon reduces aqueous Hg to <1 ng L-1, outperforming thiol-functionalized activated carbon by two orders of magnitude. Efficacy persists under pH variations, dissolved organic matter, and ionic interference, with structural/functional stability maintained after 30-day exposure to corrosive media. Geobacter sulfurreducens PCA pure-culture experiments demonstrate immobilized mercury resists microbial methylation (94.3% less methylatable Hg than conventional activated carbon). Soil incubation under simulated flooded conditions confirms 96.6% porewater Hg, 97.1% porewater methylmercury, and 93.9% soil methylmercury reduction at 1 wt% loading. Notably, 0.01 wt% achieves efficacy matching standard activated carbon, demonstrating outstanding mercury immobilization.

Dissolved organic matter (DOM) is a vital component of the carbon cycle in freshwater ecosystems, including small water bodies such as urban ponds. This study investigated the effects of duckweed on DOM in such ponds. Field observations revealed that duckweed-covered ponds had reduced light penetration and oxygen availability, inhibiting DOM photodegradation and microbial degradation. Duckweed may also contribute to persistent DOM. A multi-property persistence index (PI) confirmed greater DOM persistence in duckweed-covered ponds, consistent with the optical property analysis. Laboratory experiments in which duckweed was removed or added showed that duckweed-covered water had higher dissolved organic carbon, chromophoric DOM, protein- and humic-like substances, and higher PI. These findings mirrored field results. Overall, reduced sunlight and oxygen in duckweed-covered ponds hinder DOM degradation; however, duckweed itself may also contribute to persistent DOM. These findings enhance the current understanding of DOM dynamics and biogeochemical processes in small inland waters with hydrophytes, especially in artificial freshwaters, such as urban ponds.

Sulfate-driven anaerobic oxidation of methane (AOM) and anaerobic digestion (AD) with municipal wastewater sludge containing heavy metals may provide favorable conditions for the biogeochemical transformation of mercury (Hg) by methanogens and methanotrophs. However, it remains largely unclear what Hg-methylators functioned and what role Methanosarcina played in these processes. Here, we performed sulfate-driven AOM following AD with Hg-containing wastewater sludge and investigated the role of microbes, especially Methanosarcina, in the biogeochemical transformation of Hg based on 16S rRNA amplicon and metatranscriptomic sequencing. Results showed that methylmercury (MeHg) concentrations and MeHg/total Hg ratios increased significantly, implying mercuric Hg [Hg(II)] methylation predominated MeHg demethylation. Desulfovibrio, Desulfobulbus and Methanosarcina dominated and thus likely played important roles in Hg(II) methylation, while Methanosarcina dominated and functioned in methane metabolism. In the presence of sulfate, differentially-expressed genes (DEGs) related to Hg transporting ATPase increased significantly, indicating Methanosarcina absorbed a large amount of Hg(II) and likely further methylated it to MeHg. No Hg response DEGs were found in the absence of sulfate, further confirming sulfate played an essential role in Hg cycle. Overall, these results suggest that controlling sulfate levels and Methanosarcina abundances in municipal wastewater could potentially mitigate MeHg risks to humans.

The consumption of rice enriched with methylmercury (MeHg) is one of the important exposure routes, posing threats to human health. However, metabolic responses of different rice varieties to soil MeHg remain unclear. Here, we analyzed the changes in root metabolites of high- (H699) and low-accumulating (H777) rice varieties under MeHg stress via untargeted metabolomics. MeHg (0.9 μg g-1) led to a significant increase in oxidative damage and antioxidant enzyme activities in leaves, suggesting leaves are more sensitive to MeHg. Distinct metabolite profiles occurred in rice roots under MeHg stress, with H699 predominantly involving lipid metabolism pathways, whereas H777 engaged amino acid metabolism pathways. Two key metabolites, silymarin and 12-hydroxylauric acid can effectively alleviate MeHg stress in rice by reducing MeHg accumulated in rice roots by ∼85 %. Overall, this study provides key targets and foundations for breeding low-MeHg, tolerant rice, crucial for reducing grain MeHg, ensuring safety, and protecting health.

The forest ecosystem is a significant pool for capturing atmospheric mercury (Hg) deposition, with most Hg accumulating in forest soils. As secondary forests now dominate global forest cover, they are particularly sensitive to changes in ambient temperature. However, the impact of these changes on Hg dynamics in secondary forests remains poorly understood. Here, we quantified Hg inputs, outputs, and mass balances in two secondary forests in China, each with different ambient temperatures. We found that elevated ambient temperature (similar to 1.0 degrees C) advanced the germination of leaves by 2-3 days and extended the growing season by approximately one week, resulting in increased litterfall biomass by 1.18 Mg hm(-2) yr(-1) and a thicker litterfall layer by 0.22 cm over 34 years. This temperature rise also facilitated Hg methylation within forest and enhanced methylmercury (MeHg) export, heightening the potential risk of MeHg exposure to surrounding ecosystems. Additionally, higher ambient temperature not only increased soil Hg emissions (2.75 mu g m(-2) yr(-1)) but also led to significant Hg deposition via litterfall (9.26 mu g m(-2) yr(-1)), resulting in a net annual Hg deposition of 6.88 mu g m(-2) yr(-1). This net Hg deposition accumulated in the topsoil, increasing the Hg pool by 0.51 mg m(-2) in organic and 0-10 cm mineral soil horizons. Our findings suggest that even a similar to 1.0 degrees C temperature rise could enhance the role of secondary forests as atmospheric Hg sink by 45.10 %. Therefore, the impact of ongoing climate warming on Hg cycling and pools in forests should receive increased attention and warrants further research.

Alpine timberline ecotones are climatically sensitive transition zones, where small but persistent variations in temperature can markedly affect soil organic matter (SOM) composition, persistence, and the retention of pollutants such as mercury (Hg). While SOM-Hg interactions have been extensively studied in different ecosystems, the molecular-level mechanisms governing these relationships in high-elevation timberline ecotones remain unclear. Here, we investigated SOM molecular composition, persistence, and soil Hg content in the lower (LT) and upper (UT) timberline of Mt. Gongga, China. We applied pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) to characterize SOM molecular components, calculated a persistence index (PI) using the multifunctionality method from 18 SOM persistence-related properties to quantify resistance to decomposition, and measured total Hg concentrations using cold-vapor atomic fluorescence spectrometry. The significantly higher carbohydrates and lignin at LT indicate higher incorporation of fresh plant inputs than at UT. In contrast, the predominance of aliphatic SOM at UT suggested enhanced microbial processing. The significantly higher PI at LT indicated greater SOM persistence in this zone. Interestingly, SOM-Hg coupling was stronger at UT, even though total Hg levels were higher at LT, suggesting less effective Hg retention at LT. These findings indicate that LT serves as a key zone for carbon and Hg storage, whereas UT exhibits stronger SOM-Hg associations. With projected upward timberline migration under global warming, alpine soils may sequester more carbon and Hg, but weakened SOM-Hg coupling could increase Hg mobilization risks. These findings advance the understanding of SOM-Hg interactions by integrating molecular composition and persistence metrics into natural climate gradient studies, providing a novel framework for predicting Hg mobility risks under timberline migration driven by global warming.

Heavy metals (HMs) in suspended particulate matter (SPM) present critical ecological and health concerns due to their mobility, bioavailability, and toxicity in aquatic systems. However, the speciation and associated ecological risks of HMs in freshwater SPM remain inadequately characterized. This study investigated the concentrations, speciation, and ecological risks of ten HMs (Cr, Ni, Cu, Zn, As, Cd, Pb, Mn, V, and Co) in paired SPM-sediment matrices across five representative small and medium-sized lacustrine and fluvial ecosystems in Southwest China, using a modified European Community Bureau of Reference (BCR) sequential extraction method combined with multiple risk assessment approaches. Results showed that Mn exhibited the highest enrichment in SPM, with concentrations 8.8-fold higher in lake systems and 2.6-fold higher in river systems compared to sediments. BCR analysis further revealed that, compared to sediments, SPM had a higher proportion of reducible fractions, implying the presence of substantial amounts of recently formed, authigenic Mn oxides in SPM. Geoaccumulation index (Igeo) indicated that Cd, Mn, and Zn were the predominant contaminants in SPM across all systems. These three metals exhibited the highest proportions in the exchangeable fraction, and SPM contained greater exchangeable fractions than sediments, suggesting enhanced mobility and bioavailability. Multidimensional risk assessment demonstrated that SPM-associated metals, especially Mn, posed greater ecological and health risks (particularly for children) than those in sediments. Overall, this study highlights SPM as both a carrier and a secondary source of HMs in freshwater systems, underscoring the need for targeted monitoring and management strategies to reduce labile HM inputs and protect aquatic ecosystem health.

Phytoremediation offers a sustainable strategy for mitigating mercury (Hg) contamination, yet its efficacy under variable water availability remains poorly understood. Robinia pseudoacacia, a leguminous tree with notable phytoremediation potential, was investigated under combined Hg exposure and water stress-drought (HgD) or flooding (HgF)-with or without rhizobia inoculation. In a controlled greenhouse study, HgD exposure enhanced root dry biomass, increased nodule nitrogenase activity, and promoted root Hg accumulation, indicating a detoxification mechanism via root retention. In contrast, HgF suppressed plant growth and nitrogen fixation, reduced total Hg uptake, and increased Hg translocation to shoots, suggesting redistribution to protect root function. Multi-omics analyses revealed that both HgD and HgF induced genes involved in cysteine and methionine metabolism (e.g., GSS, GCLC, ACS), enhancing thiol-mediated Hg detoxification and altering sulfur allocation. L-serine biosynthesis was consistently downregulated. Hormonal responses diverged: HgD suppressed jasmonic acid biosynthesis (downregulation of AOS, AOC) and reduced 12-OPDA levels, whereas HgF activated α-linolenic acid oxidation, elevating 12-OPDA and its derivatives (e.g., colneleic acid). Rhizobial inoculation further improved root Hg retention, upregulated antioxidant enzymes (SOD, POD), and maintained membrane integrity. Under HgD, inoculation enhanced phenylpropanoid metabolism (upregulation of PAL, CCR, CAD), promoting lignification. Under HgF, it stimulated the pentose phosphate pathway (via PFK induction), optimizing carbon flux for stress resilience. These findings demonstrate that Robinia-rhizobia symbiosis mediates distinct physiological and metabolic reprogramming under drought and flooding, enabling context-specific Hg detoxification. This highlights Robinia's potential as a robust phytoremediator in Hg-contaminated environments with fluctuating water regimes.

The electron-donating capacity (EDC) of dissolved organic matter (DOM) plays a central role in regulating environmental redox processes, and is closely governed by the DOM characteristics. As DOM increasingly becomes a focal point in carbon sequestration strategies aimed at mitigating climate change, understanding how its molecular characteristics influence redox functionality is critical. However, the role of DOM chemodiversity, including molecular diversity, functional diversity, and compositional traits, in governing its EDC remains underexplored at the molecular scale. In this study, representative allochthonous, autochthonous, and mixed DOM samples were analyzed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), UV-Vis spectroscopy, and excitation-emission matrix fluorescence spectroscopy. The EDC was quantified using a decolorization assay based on ABTS reduction. Results showed that EDC was not significantly correlated with overall molecular diversity, but was strongly associated with the relative abundance of polyphenolic, highly aromatic, and unsaturated compounds. These molecules also exhibited greater persistence and formed highly interconnected and thermodynamically constrained transformation networks, indicating a structural trade-off between redox functionality and degradability. This structure-function-persistence relationship implies that changes in DOM stability during carbon sequestration may significantly influence its redox capacity, thereby modulating key environmental processes such as metal cycling, and contaminant fate. By elucidating the molecular-level linkages between DOM chemical traits and electron-donating activity, this study reveals how structural characteristics govern redox functionality, emphasizes the dominant role of composition over diversity in regulating DOM reactivity, and highlights potential ecological risks relevant to carbon stabilization strategies.