Influence mechanism of tritium exposure on the growth and microcystin synthesis of Microcystis aeruginosa under rising temperature.

To advance aquatic ecological risk assessment, this study investigated synergistic physiological and molecular responses of the Microcystis aeruginosa to combined heatwave and tritium co-exposure, against a backdrop of increasingly frequent global heatwaves and continuous tritiated radioactive wastewater discharge.A tritium level of 3.7×104 Bq/L, typical of nuclear plant wastewater, was used to examine tritium's mechanistic impacts on Microcystis aeruginosa growth and microcystin production under simulated warming (25, 30, and 35 °C). Combined heatwave and tritium exposure induced prominent synergistic toxic effects and disrupted cellular antioxidant homeostasis. Single heat treatment (30 °C) stimulated algal growth yet repressed transcription of the microcystin biosynthetic gene cluster (mcyA-mcyJ). Separate tritium exposure (3.7×104 Bq/L) raised extracellular MC-LR release by 58.3%. Co-exposure damaged Photosystem II, depleted the MC-LR precursor L-arginine, and disrupted the TCA cycle to jointly reduce intracellular microcystin accumulation. After recovery, co-exposure groups exhibited a 25.72% reduction in intracellular MC-LR alongside remodeled photosynthesis and altered toxin distribution. Extreme heat-tritium co-stress lowered microbial alpha diversity and enriched stress-tolerant archaea, with cyanobacterial abundance negatively correlated to extracellular MC-LR. Heatwave-tritium co-exposure disrupts MC-LR synthesis and release via suppressed toxin biosynthesis, rewired energy metabolism, and reshaped microbial communities.