Phase-Dependent Effects of Photoperiod on Growth and Microcystin-LR Production in Two Microcystis Strains: Insights from Batch Culture for Bloom Management

Wenqing Xiao (), Xiaojing Wang and Long Wang
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Wenqing Xiao: Jiangxi Provincial Key Laboratory of Safe and Efficient Mining of Rare Metal Resource, School of Emergency Management and Safety Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China
Xiaojing Wang: Jiangxi Provincial Key Laboratory of Safe and Efficient Mining of Rare Metal Resource, School of Emergency Management and Safety Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China
Long Wang: Jiangxi Provincial Key Laboratory of Safe and Efficient Mining of Rare Metal Resource, School of Emergency Management and Safety Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China

Sustainability, 2025, vol. 17, issue 22, 1-17

Abstract: The escalating threat of cyanobacterial blooms necessitates a deeper understanding of the environmental factors regulating their toxicity. While light intensity effects are well-documented, it remains unclear whether photoperiod regulates microcystin (MC) production. This study investigates the effects of five light–dark (LD) cycles on the growth and MC-LR production of two Microcystis strains in batch culture under a light intensity of 25 μmol m −2 s −1 . Longer photoperiods enhanced early growth, although long-term biomass accumulation proved strain-dependent. Regarding toxin production, cellular MC-LR (total toxin per cell) during the initial 9-day phase was analyzed using a mixed-effects model. The analysis revealed significant main effects of photoperiod and cell density, supporting both direct and growth-mediated indirect effects of photoperiod. Moreover, a significant strain × photoperiod × day interaction ( p < 0.001) was observed, indicating additional strain-specific and time-dependent regulation. Conversely, a general linear model of the strictly intracellular MC-LR at the 27-day endpoint showed significant independent effects of photoperiod and cell density, with no interaction. The photoperiod effect strengthened after controlling for cell density. These findings reveal a phase-dependent regulation of toxicity, suggesting that risk assessment based solely on biomass is inadequate. Sustainable bloom management should therefore incorporate photoperiod dynamics and adopt phase-specific strategies.

Keywords: Microcystis; microcystin-LR (MC-LR); light–dark cycle; photoperiod; water management (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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