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Biodiversity change has elicited widespread concern over the consequences for functions and services provided by ecosystems1-3. Despite extensive evidence for a positive effect of biodiversity on ecosystem functioning within a single trophic level4,5, how this biodiversity effect varies with multi-trophic food web structure remains unresolved6 even though most ecosystems contain two to six trophic levels7. We investigate how food web complexity modulates biodiversity-ecosystem functioning relationships in nature by quantifying energy fluxes as proxies for two principal ecosystem functions8-primary consumption and predation-in 318 highly resolved, complex food webs from marine, lake, stream and soil ecosystems. Ecosystem functioning increased consistently with taxon richness across all trophic levels and ecosystems, which arose from greater vertical diversity (that is, maximum trophic level9) and trophic complementarity of predators in more taxonomically diverse food webs. Furthermore, predator trophic complementarity10,11 increased predation fluxes in all freshwater ecosystem types. These findings highlight the threat of trophic downgrading to critical ecosystem functions (for example, biological control and maintenance of biodiversity and ecosystem stability) provided by predators12,13, which are typically most vulnerable to anthropogenic disturbances14,15. Our study demonstrates that the consequences of biodiversity change are deeply entangled within the web of life, emphasizing the need to conserve the trophic complexity underlying biodiversity-ecosystem function relationships.

Bencomia exstipulata is a broad-leaved evergreen shrub endemic to the high-altitude harsh landscapes of the Canary Islands. Whether the extremely reduced distribution of its wild specimens (at around 2000 m a.s.l. in the National Parks of 'El Teide' and 'Caldera de Taburiente') responds to specific microclimatic needs remains undetermined. None of its ecophysiological aspects has been evaluated to date. To fill this gap of knowledge, we have (1) characterised its leaf phenology and physiology, (2) evaluated its tolerance to drought at leaf and xylem levels, and (3) investigated its response to freezing stress at biophysical and photochemical levels. Our results revealed that B. exstipulata has a fast leaf turnover with high rates of photosynthesis and stomatal conductance and high xanthophylls per chlorophyll ratios. Leaves had thin cuticle, high minimum leaf conductance, and encrypted and abaxial stomata. Adult leaves lost 50% of their rehydration capacity at around 45% relative water content, and stem xylem was relatively vulnerable to embolism (with -3 MPa of water potential at 50% loss of conductivity), but no native embolism was found. Under freezing temperatures, leaves showed a supercooling strategy (ice nucleation at -14°C) and low photoprotective responsiveness. We conclude that B. exstipulata lacks clear adaptations to drought, has high constitutive photoprotection, low photoprotective responsivity, and a supercooling strategy to face freezing. In its native montane ecosystem, with a Mediterranean-type climate, severe drought could induce significant xylem-embolism, while severe freezing could lead to irreparable leaf damage, being both risks potentially lethal in the mid- to long term.

We introduce a recurrent inference framework for the Classification and Reconstruction of Overlapping Patterns (CROP) in mixtures formed by overlapping two patterns drawn from the same distribution. The framework alternates between bottom-up classification and top-down generative reconstruction within an iterative inference procedure. At each iteration, the method estimates the most likely class present in the mixture, reconstructs the corresponding signal using a conditional generative model, and applies a mask to isolate that component. This classification-guided reconstruction progressively separates the overlapping signals while also producing their class labels. The objective is therefore to iteratively separate and classify the overlapping patterns rather than perform general blind source separation. An important feature of the framework is that the generative model can be trained using only clean samples, without requiring paired mixed-clean training data. The iterative procedure implicitly implements a form of attention in which saliency- and priority-driven estimates guide the masking and reconstruction of individual patterns. Experimental results on mixtures of handwritten digits show that the proposed framework can successfully separate and classify overlapping patterns through this iterative classification-reconstruction process.

Phlegmariurus cruentus, a member of the Lycopodiaceae family, is a phytochemically unexplored species that is native to the high Andean forests of Colombia and Venezuela. Herein, serratene-type triterpenoids were detected in the ethanol extract of P. cruentus via LC-ESIMS, and subsequent bioassay-guided fractionation performed using the Artemia salina lethality assay yielded four new serratenes (1-4) along with six known analogs (5-10). The structures of the isolated compounds were elucidated by HRESIMS, IR, 1D and 2D NMR spectroscopy, optical rotation, and a comparison with reported data. The in vitro cytotoxic activity of compounds 1-9 against three human cancer cell lines (U87-MG glioblastoma, MCF-7 breast carcinoma, and HT-29 colon adenocarcinoma) was evaluated using the MTT assay. Compounds 1, 5, 7, and 8 exhibited significant cytotoxicity against the U87-MG and MCF-7 cells, with IC₅₀ values ranging from 1.1 ± 0.6 to 9.6 ± 2.6 μM. Notably, compared with the other two cell lines, the U87-MG cells were more sensitive to these compounds. A further flow cytometry investigation revealed that compounds 1, 5, 6, 7, and 8 manifested proapoptotic effects in the U87-MG cells. Additionally, a GC-MS analysis of the less polar chromatographic fraction led to the identification of two know cytotoxic volatiles, α-tocospiro A and α-tocospiro B, which are reported here in the Lycopodiaceae family for the first time. These findings suggest that some compounds from P. cruentus may serve as promising candidates for further anticancer research.

NPTN encodes human neuroplastin (hNp), a transmembrane immunoglobulin (Ig)-superfamily glycoprotein and a subunit of the plasma membrane calcium (Ca2+)-ATPases (PMCA). The critical importance of hNp and its associations with PMCA in the human brain remains unknown. Here, we describe de novo NPTN variants in individuals with autism and mild-to-severe DD/ID and evaluate their effects using animal models and in silico, molecular, and cellular approaches. Four individuals present variants affecting the two hNp isoforms, hNp55 and hNp65. Other four variants affect only the hNp65 isoform. Two individuals independently carry the same loss-of-function nonsense variant, predicted to cause haploinsufficient production of all hNp isoforms. Haploinsufficient Nptn+/- mice displayed reduced levels of Np and PMCA and exhibited altered social behavior. Insufficient Np55/65 production in neurons resulted in reduced PMCA expression and function. Two missense variants caused particular structural and thermodynamic abnormalities and lower expression of hNps in human embryonic kidney (HEK) cells. In primary neurons, these hNp variants failed to regulate cytosolic Ca2⁺ transients. In Drosophila, a missense mutation affecting the PMCA interaction failed to prevent the lethal phenotype caused by hNp ortholog elimination. We show that a novel neurodevelopmental disorder characterized by intellectual disability and autism originates from haploinsufficient NPTN gene dosage or insufficient functionality of mutant hNp related to PMCA hypofunction.

Hepatoblastoma (HB) is the most common primary liver malignancy in childhood, yet its molecular determinants, functional dependencies, and therapeutic vulnerabilities remain incompletely characterized. Integrative analyses combining transcriptomic profiling with functional genomic datasets provide a strategy to identify essential genes, biomarkers predictive of tumor behavior and treatment response. Differential expression analysis comparing HB tumors with normal liver was processed on training cohort. These genes were integrated with DepMap CRISPR-Cas9 dependency scores to prioritize HB-essential candidates. Elastic Net regression was used to derive a 16-gene predictive signature, which was validated in an external cohort. Single-cell RNA-seq datasets were analyzed to assess expression patterns across hepatic and tumor-associated cell populations. A supervised deep-learning classifier was trained on single-cell profiles to distinguish tumor cells from hepatocytes, and SHAP values were computed to interpret gene contributions. Drug-gene interactions were queried using curated repressive compounds from DGIdb, and approved drugs were screened for relevance in pediatric cancer clinical trials. A total of 789 genes were found overexpressed in HB tumors from the training transcriptome cohort. Chronos DepMap analysis identified 73 HB-essential genes that were not essential in adult liver cancer cell lines (hepatocellular carcinoma and cholangiocarcinoma). Elastic-net tuning based on the expression of 16 HB-essential genes in the split training cohort enabled robust tumor-normal discrimination, with AUC = 0.88, specificity = 0.90, and sensitivity = 0.90 in internal validation. This performance was confirmed in an independent external cohort, achieving AUC = 0.99, specificity = 1.00, and sensitivity = 0.98. Single-cell validation further demonstrated tumor-specific enrichment of the signature. The deep-learning classifier (tumor cells vs. normal hepatocytes) reached high accuracy (AUC = 0.99; F1-score = 0.97), with SHAP analysis highlighting PEG10, GREB1, PLCB4, RHOBTB1, CRIM1, FSD1L, CORO2A, KIT, ANKRD50, HDAC11, ZNF233, SEMA7A, and FABP4 as major contributors. Six of these genes were confirmed to be absent or lowly expressed in the background liver microenvironment. Drug-gene interaction analysis identified HDAC11 as a potential therapeutic target of approved drugs used in pediatric oncology. This integrative framework combining transcriptomics, CRISPR dependency mapping, machine learning, and pharmacogenomic annotation identifies clinically relevant HB-essential genes and predictive molecular signatures for tumor identity. The derived expression-based scores provide tools for patient stratification, while drug-gene mapping highlights actionable vulnerabilities on HDAC11 with pediatric approved drugs that support rational drug repurposing strategies in hepatoblastoma.

Soil microbiomes are critical for ecosystem functioning, yet the global influences of climate and agricultural practices on their diversity and structure remain incompletely characterized. Here we analyzed 1921 soil samples from 33 countries worldwide across diverse biomes to assess how climate gradients and agricultural inputs, including pesticides and fertilizers, shape prokaryotic and fungal communities. We found that microbial diversity peaks at intermediate temperatures and differs markedly between natural and agricultural soils, with agriculture increasing microbial diversity while altering community composition and ecological guilds. Pesticide use selectively reduced bacterial diversity and shifted fungal guilds, decreasing ectomycorrhizal fungi while increasing saprotrophs, whereas fertilization reduced microbial network cohesion, with organic and inorganic fertilizers eliciting distinct community responses. These findings reveal that climatic factors and agricultural management jointly influence soil microbial diversity, community structure, and network connectivity, with implications for soil health and ecosystem resilience in managed landscapes. Overall, our results demonstrate that agricultural practices, including the use of pesticides and both organic and inorganic fertilizers, act as strong ecological filters that reshape soil microbiomes worldwide-enhancing apparent diversity but driving a functional shift toward less mutualistic, more fragmented, and potentially less resilient communities.

Obesity is a global public health issue, increasingly affecting young adults. Its association with other diseases highlights the urgency of developing prevention strategies. Genetic factors play a significant role in susceptibility to obesity, making the identification of risk-associated variants essential for prevention strategies. Therefore, this study aimed to analyze LEP, LEPR, and FTO variants as potential genetic risk factors for obesity in Brazilians aged 18-35 years. The participants were classified with, or without obesity/overweight. Genotyping was performed by ASO-PCR, RFLP, and DNA sequencing. A questionnaire was applied to collect anthropometric data, and personal and family medical history. Preliminary analyses indicated that obesity was significantly associated with individuals over 25 years of age; therefore, to specifically investigate early-onset obesity, the primary genetic association analyses were restricted to the 18-25 age group. A significant association was found between the LEP rs7799039 variant and BMI ≥ 25 Kg/m², and LEP rs17151919 was strongly associated with BMI ≥ 30 Kg/m² in this age group. These findings underscore the importance of identifying genetic variants that increase the risk of obesity in young adults and suggest contributing to the development of more effective and personalized prevention strategies, integrating knowledge from genetics, medicine, and nutrition.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor originally characterized as a mediator of xenobiotic detoxification. Growing evidence now establishes AhR as a central integrator of metabolic, immune, and environmental signals in the central nervous system (CNS). Beyond toxicological responses, AhR regulates neural development, glial programming, neuroendocrine function, synaptic plasticity, and barrier integrity across the lifespan. During embryogenesis, AhR contributes to lineage specification, neurogenesis, and circuit assembly through transcriptional and epigenetic mechanisms. In the adult CNS, AhR preserves cognitive resilience and circuit stability by shaping microglial and astroglial phenotypes, regulating neurotransmission, neurogenesis, myelination, and circadian timing. Dysregulation of AhR signaling by genetic, inflammatory, microbial, and environmental cues disrupts these homeostatic programs and increases vulnerability to CNS dysfunction. Pathologically, AhR exerts context-dependent dual functions, constraining neuroinflammation and supporting tissue repair in some settings while amplifying oxidative stress, barrier disruption, and neuronal loss in others. Finally, ligand-directed programming of AhR signaling emerges as a promising therapeutic framework for CNS disorders. Collectively, this review positions AhR as a ligand-sensitive regulator of CNS homeostasis and disease, while highlighting its broader relevance as a systemic regulator of physiological and pathological processes beyond the nervous system.

This study aimed to evaluate the anticryptococcal activity of the ethyl acetate fraction (FAMu) from the ethanolic extract of Myracrodruon urundeuva bark. The extract was fractionated and subjected to in vitro cytotoxicity and minimal inhibitory concentration (MIC) tests. After screening, FAMu was selected for further testing: phytochemical composition, antifungal susceptibility, synergy with fluconazole and amphotericin B, kill-curve assay, effects on cell morphology and capsule, alterations in ergosterol content, and induction of oxidative burst. The alternative invertebrate model Tenebrio molitor was used to evaluate in vivo toxicity, survival, and fungal burden. The LC-UV/DAD-ESI/MS fingerprint identified phenolic compounds such as chlorogenic acid, apocynins, cinchonaines, and urundeuvins. FAMu had a selectivity index between 16 and 32 and MICs below 13 µg mL-1. Synergy tests revealed indifferent interaction with standard antifungals. FAMu exposure was associated with reduced fungal viability after 24 h, alterations in ergosterol content, lipid peroxidation, reduced capsule size, and changes in cell surface charge. In vivo assays showed that the infected larvae had a more favorable outcome when treated with FAMu alone or combined with fluconazole. FAMu demonstrated anti-cryptococcal activity in vitro and in the T. molitor model. These results suggest that phenolic-rich fractions from M. urundeuva could be a valuable source of compounds for further antifungal research. However, additional studies are needed to validate these findings in mammalian models and assess their potential applicability.

Sagittaria montevidensis is an aquatic macrophyte distributed across South America, especially in southern Brazil. In this study, we report the first confirmed record of this species in northeastern Brazil, based on collections from irrigated rice fields in Arari (Maranhão State). The populations observed at the study sites exhibit vigorous active reproduction and show patterns warranting evaluation of possible herbicide resistance, indicating strong potential for establishment and spread in the region. Considering the species' large geographic disjunction, long-distance dispersal by waterbirds emerges as the most plausible introduction pathway for Maranhão. We provide a morphological description, photographs, and an updated distribution map for the species in Brazil. We also discuss the environmental conditions that favor its establishment and the potential ecological and agronomic implications of its introduction.

Staphylococcus aureus is a major opportunistic pathogen associated with dairy production systems, where it contributes to intramammary infections and may enter the food chain through contaminated milk. The increasing prevalence of antimicrobial-resistant strains underscores the need for alternative biocontrol strategies. Here, we report the isolation and comprehensive characterization of a novel lytic bacteriophage, vB_SauP-INT105, obtained from wastewater in Extremadura, Spain. Plaque morphology revealed a distinctive three-zone halo pattern suggestive of phage-encoded exopolysaccharide depolymerase activity, confirmed by bioinformatic prediction of two candidate depolymerase-encoding ORFs. Electron microscopy showed a bacteriophage with an icosahedral head and a short non-contractile tail. The phage exhibited lytic activity against 86.5% of 37 dairy-associated S. aureus isolates tested. One-step growth analysis revealed a latency period of ~40 minutes and a burst size of ~23 PFU/cell. The phage showed robust stability across a wide range of temperatures and pH values relevant to dairy-processing conditions, retaining viability over 20 months at 4 °C. Genome sequencing revealed a 17.45 kb dsDNA genome encoding 20 ORFs, with no detectable genes associated with virulence, lysogeny, or antibiotic resistance. Phylogenetic analysis placed INT105 as a novel species within the Rosenblumvirus genus. Antibiofilm assays demonstrated significant reductions in viable cell counts in two S. aureus strains with contrasting biofilm phenotypes. These results establish INT105 as a genomically safe, environmentally robust and functionally effective phage with strong potential for biocontrol applications in dairy-production environments and broader food-safety and clinical contexts.

Granulosa cell function is essential for proper ovarian physiology. Redox imbalance compromises granulosa cell survival, thereby impacting follicle fate within the ovary. Humanin (HN), a small mitochondrial-derived peptide, exerts cytoprotective effects in several tissues under pro-oxidant conditions. The present study aimed to evaluate the cytoprotective effects of HN under oxidative conditions in granulosa cells, using a human granulosa cell line (KGN) and an in vitro rat ovary culture to assess its action within the ovarian microenvironment. KGN cells showed a significant increase in endogenous HN mRNA expression in response to oxidative conditions induced by H2O2. Upon oxidative insult, exogenous HN enhanced cellular antioxidant capacity by significantly increasing catalase (CAT) activity levels, without modifying superoxide dismutase (SOD) expression or activity, or redox status in KGN cells. Importantly, HN significantly decreased H2O2-induced granulosa cell apoptosis in KGN cells, as determined by the TUNEL assay. This protective effect was associated with modulation of key apoptosis-related genes, including reduced expression of BAX and the caspase-3 precursor (CASP3), while BCL2 expression remained unchanged. Consistently, in rat ovaries, HN protected granulosa cells of antral follicles under oxidative conditions. In conclusion, our findings support a cytoprotective role of HN in granulosa cells under oxidative conditions, which may contribute to the maintenance of antral follicle survival within the ovarian microenvironment.

Replication stress poses a major threat to genome integrity, yet how higher-order chromatin organization contributes to replication fork protection remains unclear1,2. Here we show that replication stress induces the formation of transient chromatin loops that enclose de novo heterochromatin-enriched stalled replication forks3. Stressed forks preferentially stall at convergent CTCF motifs, triggering stress-dependent CTCF enrichment that constrains loop extrusion and stabilizes these structures. Loop stabilization requires both CTCF anchoring and G9a-dependent heterochromatin (trimethylation of Lys9 of histone H3 (H3K9me3)) deposition on nascent DNA within the loop body. These loops function as protective scaffolds that shield stalled and reversed forks from degradation by multiple nucleases. By contrast, combined loss of stress-induced heterochromatin and CTCF enrichment destabilizes the loop scaffold, exposing multiple entry points for nucleolytic attack and resulting in extensive nascent-strand degradation through mechanisms distinct from classical fork-reversal-dependent pathways. This protective architecture is similarly critical in BRCA2-deficient cells, in which replication-stress-associated loops predominantly safeguard replication initiation zones, while nascent DNA outside these loops undergoes massive degradation and remains highly susceptible to mutations. Our study elucidates the fundamental role of replication-stress-induced three-dimensional genome reorganization in preserving replication fork stability, thereby mitigating mutagenesis and genomic instability.

BackgroundSystemic lupus erythematosus (SLE) features aberrant T-B cooperation and expansion of atypical memory B cells (aMBCs) characterized by the expression of CD11c and T-bet. We investigated the relationship between IL-21/IL-21R and the activation state of cTfh and Tph, with CD11c+T-bet + B cell subsets and clinical activity.MethodsA cross-sectional study was conducted involving 40 patients with systemic lupus erythematosus (SLE) and 15 healthy subjects (HS). A multiparameter flow cytometry was used to evaluate Tph (CD4+CXCR5-PD-1+), cTfh (CD4+CXCR5+PD-1+), and aMBCs (CD19+CXCR5-CD11c+) subsets and intracellular expression of IL-17A (iIL-17A), IL-21 (iIL-21), and T-bet. The disease activity was assessed using the SLEDAI-2K.ResultsWe found an increased frequency of cTfh PD-1vh, HLA-DR+, IL-21R+, and Tph PD-1vh, HLA-DR+, and iIL-21+ cells in SLE patients. The aNAV T-bet+ cells were expanded in SLE patients. Activated T-cell states (iIL-21+/IL-21R+/PD-1vh/HLA-DR+) correlated with T-bet+ B cells subsets. Finally, activated cTfh/Tph and aMBCs correlated with SLEDAI-2K.ConclusionsOur findings provide new insights into the cooperative expression of IL-21/IL-21R and T-bet and their potential relationships with extrafollicular B-cell responses in SLE. These results highlight the IL-21/T-bet axis, offering potential avenues for biomarker development and targeted therapeutic intervention in SLE.

The genus Senecio comprises more than 1,200 species, at least 25 of which are known to be toxic due to the presence of pyrrolizidine alkaloids. In Brazil, approximately 68 species occur, predominantly in rural and mountainous regions. This study was performed to investigate the specialized metabolites of Senecio oleosus using isolation and dereplication strategies and to evaluate their antiproliferative activity against tumor cell lines. A phytochemical investigation of S. oleosus was conducted using various chromatographic techniques. Structural elucidation was based on spectroscopic analyses and comparison with literature data. Dereplication was performed using UHPLC-HRMS/MS. Molecular networking was generated through GNPS2 and analyzed using Cytoscape. Antiproliferative activity was assessed using the MTT assay. The study led to the isolation of three new esterified shikimic acid derivatives. Dereplication of pyrrolizidine alkaloids was guided by the diagnostic fragment ions at m/z 120 and m/z 138. Diagnostic ions for esterified shikimic acid derivatives were established based on the fragmentation patterns observed in the MS/MS spectra of the isolated compounds. Molecular networking analysis enabled the annotation of 36 additional putative esterified shikimic acid derivatives. One triesterified shikimic acid derivative exhibited promising antiproliferative activity against the HCT-116 cell line, with an IC50 value of 10.5 µg.mL- 1 (20.2 µM). In total, 82 compounds were identified in S. oleosus. Except for N-oxide retrorsine and N-oxide senecionine, all compounds are reported for the first time in this species. Esterified shikimic acid derivatives emerged as the major group of specialized metabolites in S. oleosus, and triesterified derivatives demonstrated promising antiproliferative activity.

Understanding the coordination between root and shoot hydraulics is fundamental for improving plant performance under water stress. We used the Arabidopsis thaliana double mutant epf1 epf2, which displays elevated stomatal density and transpiration rate, to investigate how root hydraulics is influenced by enhanced transpiration. Mutant and wild-type (Col-0) plants were grown hydroponically under control and osmotic stress conditions, imposed by adding 2% polyethylene glycol to the nutrient solution. Both genotypes were compared for stomatal traits, water relations and aquaporin expression. Relative to Col-0, the epf1 epf2 mutant displayed ~150% higher stomatal density, but stomatal conductance and rosette water loss increased by only ~30%. Despite greater water loss and a more negative leaf osmotic potential, the mutant maintained leaf relative water content, while root osmotic potential remained similar between genotypes. Under control conditions, epf1 epf2 exhibited lower root hydraulic conductivity (Lpr) than Col-0. However, aquaporin transcript levels and the relative contribution of aquaporins to root water transport did not differ between genotypes. Under osmotic stress, the pattern reversed: Col-0 showed lower Lpr than epf1 epf2, without detectable differences in aquaporin expression or relative contribution. These results are consistent with an active role of the root in modulating whole-plant hydraulic balance. Across the tested conditions, both stomatal aperture and Lpr declined under scenarios expected to challenge plant water balance. We propose that enhanced transpiration may increase xylem tension, which could act as a long-distance signal coordinating reductions in stomatal aperture and root hydraulic conductivity, constraining water flux and stabilizing plant water status.

Understanding shark reproductive modes is crucial for conservation, as these K-strategist species are vulnerable to overexploitation. The spiny dogfish (Squalus acanthias), a small shark listed as 'vulnerable' by the IUCN, has a 22-month gestation period and a reproductive output ranging from 1 to 21 pups per litter. This study aimed to investigate multiple paternity in S. acanthias using Single Nucleotide Polymorphism (SNP) markers. Samples from six litters, comprising 40 individuals collected in Argentina, were analyzed using a ddRADseq library. SNP markers were screened with the STACKS pipeline, and kinship and paternity were analyzed using COANCESTRY and COLONY software. Results revealed 1,021 to 1,620 SNPs per litter, with multiple paternity detected in all litters. The number of sires per litter ranged from 2 to 4. No correlation was found between litter size and multiple paternity, suggesting this behavior may enhance genetic diversity. The species' size and sex segregation, coupled with females in shallower waters, increase their vulnerability to fishing pressure. Overfishing and bycatch exacerbate the reduction in sexually mature individuals, threatening population recovery. This study highlights the need for management policies that incorporate reproductive strategies, especially for species like S. acanthias with complex life histories and low recovery rates.

Mercury is a globally distributed pollutant with significant ecological impacts. Terrestrial mosses have been widely used as Hg biomonitors, however, the mechanisms governing Hg accumulation, retention and release in these organisms remain poorly understood. This knowledge gap limits both the interpretation of biomonitoring data and the assessment of Hg ecotoxicological effects on mosses. This study investigates the deposition pathways, sources, and molecular mechanisms driving Hg accumulation in Pseudoscleropodium purum integrating isotopic, chemical, and molecular analyses. Our results showed that gaseous elemental Hg (Hg0) was the primary deposition pathway, accounting for 66% of total Hg inputs. However, following deposition, a substantial fraction of Hg0 appears to undergo oxidation within moss tissues. Together with post- depositional photoreduction, these processes reduce the remaining Hg0 fraction to only 5-35% of total Hg. Hg stable isotopes and chemical tracers provided no evidence for a major contribution from local sources such as forest fires and coal combustion, or AMDEs, suggesting that long-range atmospheric transport could be the prevailing source in the study area. Strong correlations between ∆201Hg and ∆199Hg (rho = 0.88) over a wide range of values is consistent with post-depositional photochemical reduction. Molecular analyses support that Hg accumulation in mosses is consistent with an increase in amide groups and a concurrent decrease in carbonyl groups within the extracellular space. The reverse process, amide hydrolysis, could lead to the release of previously bound Hg. These findings provide new mechanistic insights into Hg cycling in mosses, suggesting that functional groups in the cell wall and plasma membrane may influence Hg partitioning. These results challenge the assumption that mosses are reliable accumulative biomonitors, demonstrating instead that, at least for this species and under the studied environmental conditions, Hg content reflects a dynamic balance between deposition and photoreductive losses.