Drilling into the physiology, transcriptomics, and metabolomics to enhance insight on Vallisneria denseserrulata responses to nanoplastics and metalloid co-stress

Co-contamination of nanoplastics (NPs) and arsenic (As) in aquatic environments poses a serious threat to the growth of aquatic plants, but the molecular toxicity mechanism leading to this joint effect on submerged macrophytes is still unclear. Here, we investigated the physiological, transcriptomic, metabolomic responses, and organelle changes in submerged macrophyte, Vallisneria denseserrulata (V. denseserrulata), to single/combined exposure to NPs and As. Our results showed that co-exposure alters physiological traits in V. denseserrulata including chlorophyll, sugars, proteins, malondialdehyde, and antioxidant enzymes. The presence of NPs exacerbated As distribution 36.2–47.2% higher than the control in plant tissues, thus enhancing combined pollution to plants. Integration of physiological traits and differentially expressed genes via weighted correlation network analysis implicated stress-responsive candidate modules related to key enzymes, such as ribulose-bisphosphate carboxylase, alanine transaminase, aspartate aminotransferase, phosphofructokinase-1, and phenylalanine ammonia-lyase. Metabolomics profiling identified carbohydrates, amino acids, organic acids, and fatty acids. Conjoint transcriptome and metabolome analysis revealed that photosynthetic systems, energy conversion, and oxidative and antioxidant regulation are the key defensive response mechanisms for V. denseserrulata under NPs-As co-exposure. Taken together, our multi-omics study provided new molecular insights into submerged macrophytes tolerance mechanisms against combined NPs and As toxicity, highlighting potential targets for stress mitigation and biomonitoring in contaminated aquatic ecosystems.