关键词: 拉氏尖头藻, 越冬, 复苏, 沉积物, 南亚热带水库

Abstract:

[Objective] Overwintering and recruitment are critical bottlenecks in cyanobacterial bloom formation. Raphidiopsis raciborskii, a globally invasive harmful cyanobacterium, poses increasing threats to drinking water sources. However, its overwintering and recruitment mechanisms in south subtropical reservoirs remain poorly understood. This study aims to elucidate its overwintering strategies and recruitment triggers in such environments, providing a scientific basis for early warning and bloom management. [Methods] We conducted stratified field sampling in three subtropical reservoirs (varying trophic states) from January to March 2025, measuring R. raciborskii abundance in both water column and sediments, along with key environmental parameters. Concurrently, laboratory experiments were performed using a locally isolated strain (N8). A winter simulation tested the combined effects of cooling rate (slow: 0.5 ℃·d⁻¹ vs. rapid: 2 ℃·d⁻¹) and light intensity (low: 100 lx vs. normal: 2000 lx) on cell density (OD₆₈₀) and photosynthetic activity (Fv/Fm). A subsequent recruitment experiment exposed cold-acclimated cultures and sediment inocula to different temperature (15, 20, 25 ℃) and light (100, 2000 lx) combinations. Redundancy analysis (RDA) was used to identify environmental drivers of field distribution patterns. [Results] Field surveys showed that overwintering R. raciborskii biomass was predominantly retained in the water column, with minimal abundance in sediments. Its vertical distribution was reservoir-specific: in shallow reservoirs (~10 m depth), it concentrated near the bottom; in the deep reservoir (~21 m), it peaked in the middle layer (8-12 m). RDA identified water temperature, water depth, and total phosphorus as the most significant drivers (p<0.05) of its spatial distribution. Laboratory experiments revealed that under slow cooling and low light (mimicking conditions in deeper water layers), cells maintained higher photosynthetic activity and experienced slower biomass decline, indicating this as the optimal overwintering condition. In contrast, rapid cooling combined with normal light caused severe photoinhibition. For recruitment, a strong synergistic effect of light and temperature was observed. The best recovery and growth occurred at 20-25 ℃ with normal light (2000 lx). Treatments with low light (even at warm temperatures) or low temperature (even with normal light) significantly suppressed recruitment. Sediment-origin cells could germinate but exhibited only a transient, short-lived increase, failing to sustain population growth. [Conclusion] The mild winter water temperatures and stable thermal stratification of south subtropical reservoirs enable the water column, rather than sediment, to serve as the primary overwintering seed bank for R. raciborskii. This cyanobacterium survives winter by reducing metabolic activity rather than forming deep dormant stages, and its spring recruitment strictly depends on a synchronized increase in both light and temperature. Effective bloom management should therefore shift from a sediment-only focus to an integrated surveillance of both water-column and sediment inocula, and incorporate the synergistic light-temperature effect into early warning systems. These findings provide essential guidance for safeguarding drinking water resources in subtropical regions facing R. raciborskii invasions.

Key words: Raphidiopsis raciborskii, overwintering, recruitment, sediment, subtropical reservoir