Physiological and Ecological Responses of the Bloom-Forming Diatom Achnanthidium catenatum to Nutrients

Achnanthidium catenatum exhibits both epiphytic and planktonic ecological types and forms multiple large-scale diatom blooms in different drinking water reservoirs. This study determined its growth and physiological characteristics under different nitrogen (N) or phosphorus (P) conditions. The study found that N ≤ 2.5 mg/L promoted its growth, while the promoting effect weakened at ≥5 mg/L. The lag phase of the growth cycle was shorter, taking only 6 days to reach peak density; meanwhile, it showed strong adaptability to P (0.5–3.5 mg/L), with peak density occurring by approximately 12 days. It was found that N-induced blooms formed earlier and lasted longer, whereas P-induced blooms were relatively delayed, more intense, and shorter in duration. Low and high concentrations of N, as well as P concentrations (≥0.1 mg/L), significantly promoted the formation of multicellular chain colonies (p < 0.05). The percentage of chain colonies was relatively higher during the lag phase and tended to exist as single cells during the stationary phase, at which time the colloidal extracellular polymeric substance (CEPS) content was higher and significantly correlated with changes in cell density. Alkaline phosphatase activity (APA) and malondialdehyde (MDA) content varied markedly under different N or P concentrations (p < 0.05). These results reveal the potential impact of N or P variations on the bloom-forming capacity of A. catenatum.