Algicidal effects of Landoltia punctata against toxic Microcystis aeruginosa: Insights from physiological, molecular, and environmental perspectives

Abstract

The increasing frequency of Microcystis blooms highlights the urgent need for environmentally sustainable strategies to mitigate associated ecological and health risks. Floating aquatic macrophytes, particularly duckweed, have attracted attention as potential nature-based approaches; however, their effectiveness, underlying mechanisms, and environmental impacts remain insufficiently understood. Here, we show that duckweed (Landoltia punctata) exhibits potent algicidal activity against toxic Microcystis aeruginosa in a co-culture system. Within 5 days, the initial chlorophyll-a concentration (331 μg L⁻¹) decreased by 71.9%, and cell density declined by 69.7%; these reductions were accompanied by a loss of buoyancy and severe ultrastructural damage in algal cells. Photosynthetic analyses revealed asymmetric inhibition of the photosynthetic apparatus, characterized by rapid and pronounced impairment of photosystem I activity, whereas photosystem II remained comparatively resilient. This imbalance was accompanied by enhanced oxidative stress and PCD-like responses, as evidenced by elevated antioxidant enzyme activities, caspase-3(−like) activity, increased ATP levels, and DNA fragmentation. Transcriptomic analyses further revealed coordinated disruptions in carbon and nitrogen metabolism and oxidative phosphorylation, indicating metabolic and energetic imbalance. Importantly, co-cultivation with L. punctata also contributed to cyanotoxin mitigation, as extracellular microcystin-LR concentration decreased by 19.4%, accompanied by pH stabilization, turbidity reduction, and marked shifts in dissolved organic matter composition. Metagenomic analysis of the phytoplankton community revealed that duckweed reduced the absolute abundance of Cyanobacteriota while promoting eukaryotic algae in eutrophic water bodies under laboratory conditions. Collectively, this study provides insights into the multi-level mechanisms underlying L. punctata-mediated inhibition of toxic Microcystis and highlights its potential role in nature-based cyanobacterial bloom management.