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

摘要：

【目的】越冬与复苏是蓝藻水华暴发的关键环节。拉氏尖头藻（Raphidiopsis raciborskii）为全球扩张的有害蓝藻，但其在南亚热带水库的越冬与复苏机制尚不明确。本文旨在探究该区域拉氏尖头藻的越冬模式与复苏条件，为水华预警提供理论依据。【方法】选取南亚热带3座水库，于2025年1－3月进行分层采样，调查拉氏尖头藻在水体与沉积物的时空分布。同时开展室内模拟实验，设置不同降温速率（0.5、2 ℃·d⁻¹）与光照（100、2000 lx）组合，观察越冬期生理响应；并通过低温处理后，在不同温度（15、20、25 ℃）与光照条件下进行复苏控制实验，测定藻细胞密度（OD₆₈₀）及光合活性（Fv/Fm），结合冗余分析（RDA）识别关键环境因子。【结果】冬季拉氏尖头藻生物量主要留存于水体，沉积物中数量较少，其垂直分布呈水库特异性：约10 m深的较浅水库集中于底层，21 m的较深水库中峰值出现在8－12 m的中层。RDA表明水温、水深和总磷是主要驱动因子（p<0.05）。室内实验显示，慢速降温结合弱光是最适越冬环境，能有效维持光合活性。复苏严格依赖光温协同，20－25 ℃配合正常光照（2000 lx）复苏最佳；沉积物中藻类虽可萌发，但难以为继，呈短暂增长。【结论】南亚热带水库温和水温与稳定分层使水体成为拉氏尖头藻的主要越冬种源库。该藻以降低代谢而非深度休眠越冬，复苏需光温精准匹配。建议水华防控应兼顾水体与沉积物种源，并将光温协同纳入预警指标。

关键词: 拉氏尖头藻, 越冬, 复苏, 沉积物, 南亚热带水库