The cell membrane permeability, morphology, metabolomics, and gene expression of Microcystis aeruginosa under various concentrations of succinic acid (SA) were evaluated to clarify the mechanism of SA inhibition of M. aeruginosa. The results showed that SA caused intracellular protein and nucleic acid extravasation by increasing the cell membrane permeability. Scanning electron microscopy suggested that a high dose of SA (60 mg L⁻¹) could damage the cell membrane and even cause lysis in some cells. Metabolomics result demonstrated that change in intracellular lipids content was the main reason for the increase of cell membrane permeability. In addition, SA could negatively affect amino acids metabolism, inhibit the biosynthesis of nucleotides, and interfere with the tricarboxylic acid (TCA) cycle of algal cells. Furthermore, SA also affected N assimilation and caused oxidative damage to Microcystis. In conclusion, SA inhibits the growth of M. aeruginosa through multisite action. GRAPHICAL ABSTRACT

To characterize the responses of Pistia stratiotes to copper oxide nanoparticles (CuO NPs), plants were exposed to CuO NPs at nominal Cu concentrations of 0 (CK), 0.1 (T₁), 1.0 (T₂), 5.0 (T₃), and 15.0 (T₄) mg·L⁻¹. Cu accumulation and translocation, growth, photosynthetic performance, reactive oxygen species (ROS), antioxidant responses, and molecular profiles were assessed. CuO NP exposure increased root Cu accumulation and reduced Cu translocation to leaves. Relative to CK, the bioconcentration factor (BCF) increased by 301.93% at T₁ but decreased by 61.65% and 73.69% at T₃ and T₄, respectively. At T₁, leaf chlorophyll and carotenoid contents increased, while photosynthetic performance and most chlorophyll fluorescence parameters remained largely unchanged. Nevertheless, root dry weight, relative growth rate, and stress tolerance index declined. At T₃ and T₄, net photosynthetic rate (P_n) decreased by 42.62–60.88% and 52.21–60.86%, respectively, accompanied by increased superoxide (O₂·⁻) levels. Antioxidant enzyme activities also responded to exposure, while glutathione (GSH) and cysteine (Cys) contents increased at higher concentrations. Transcriptomic and metabolomic analyses of leaves after 14 d were conducted for CK, T₁, and T₃. The CK-vs.-T₁ and CK-vs.-T₃ comparisons identified 588 and 1088 differentially expressed genes (DEGs) and 166 and 352 differentially accumulated metabolites (DAMs), respectively. Comparison of transcriptomic and metabolomic results suggested associations with pectin-related cell wall processes, carotenoid biosynthesis, and hormone-related metabolism, including changes in the expression of NCED1 and other related genes, as well as in ABA-associated metabolites. Overall, the results reveal contrasting physiological responses to low and higher CuO NPs expose concentrations and identify cell wall-, carotenoid-, and hormone-related pathways for further functional investigation.

1. The natural environment is subject to increasing degradation, with heavy metals being of particular concern due to their high toxicity, resistance to biodegradation, and propensity for bioaccumu...