Optimization of Pulse Repetition Frequency for Laser Inhibition of Microcystis aeruginosa: Insights into Physiological, Biochemical, and Ultrastructural Responses

This study elucidates the critical role of pulse repetition frequency (PRF) in optimizing laser inhibition ofMicrocystis aeruginosa. Using a 355 nm laser (20 ns pulse width, 5 W average power) at 20–65 kHz, 50 kHz is identified as the optimal parameter, achieving 70.6% growth suppression by day 6 (p< 0.001) and reducing cell viability to 28.0 ± 1.6% by day 5 (p< 0.001). Photosynthetic analysis reveals severe PSII dysfunction with Fᵥ/Fₘ of 0.028, representing 91% inhibition (p< 0.001). Biochemical assays demonstrate peak reactive oxygen species generation at 1.59 (p< 0.001) and progressive lipid peroxidation with MDA of 45 nmol/L protein. Transmission electron microscopy and Evans Blue staining corroborate the complete thylakoid disintegration in abundant cells after laser treatment at 50 kHz. These findings establish PRF-dependent photothermal–photomechanical synergy as a deterministic mechanism for efficient, chemical-free algal control.