Effect of temperature and soluble reactive phosphorus on abundance of Aphanizomenon flos-aquae (Cyanophyceae)

Abstract

SUMMARY Filament density of Aphanizomenon flos-aquae (Lemmerm.) Ralfs, water temperature and soluble reactive phosphorus (SRP) were measured from April to August in 1993–1996 in Lake Barato, Hokkaido, Japan. In addition, growth characteristics and internal phosphorus (P) utilization of Aph. flos-aquae were evaluated under P limitation at three temperatures (15, 20 and 25†C) to clarify the role of internal accumulated P for its growth in the incubation experiment. The filament density was highest in early July 1994, when SRP concentration had not yet decreased and the water temperature was high. These are important factors favoring an increase in abundance of this species in L. Barato. During batch culture, the time course of the stationary phase was shortest at 25†C and longest at 15†C; the cellular C:P molar ratio was 111 under P sufficiency and increased eight- to 12-fold under P limitation. As the C:P ratio was significantly higher in the decreasing phase at 15†C, Aph. flos-aquae may be more adaptable to Plimitation at 15†C than at 20†C and 25†C. However, the low temperatures did not favor the abundance of Aph. flos-aquae in 1996. This indicates that the filament density of Aph. flos-aquae decreases before it reaches the maximum value for some reason under P limitation in L. Barato.