Eutrophication amplifies Microcystis response to increasing winter temperatures, intensifying winter blooms
摘要
Toxic Microcystis blooms often occur during summer and autumn and disappear in the winter. However, increasing observational evidence has suggested prolonged Microcystis blooms, extending into winter worldwide. The underlying mechanisms, including those associated with global warming and eutrophication, remain unclear. In this study, we examined the integrated effects of eutrophication and temperatures on the survival, regrowth, and buoyancy of Microcystis colonies in environments where temperatures were low (4, 8, 12, and 8 ± 4 °C, representing the overwintering phase) and increased to a constant 25 °C (representing the recovery phase). Our results uncovered that eutrophication exacerbates the stimulating impact of warm winter temperatures on the survival and growth of overwintering Microcystis. Low nutrients (TN:1.21 mg L−1, TP:0.064 mg L−1) suppress the survival and growth of Microcystis during overwintering and recovery phases, even when the winter temperature increases to 12 °C. In contrast, Microcystis gradually grew at 4 °C under a high nutrient treatment (TN:14.63 mg L−1, TP:0.987 mg L−1). Chlorophyll fluorescence suggested such responses were likely caused by elevated nutrients, which significantly improved Microcystis' photoprotection, limiting photodamage under low temperature and light conditions. Furthermore, nutrient enrichment enabled buoyancy recovery, allowing Microcystis to float upward during the recovery phase. These findings suggest a reduced bottleneck threshold of temperature triggering winter Microcystis blooms at higher nutrient levels, underscoring the importance of nutrient control in managing cyanobacterial blooms and lake ecosystems under climatically dynamic conditions.