Ning Xu

We compared growth kinetics of Prorocentrum donghaiense cultures on different nitrogen (N) compounds including nitrate (NO₃⁻), ammonium (NH₄⁺), urea, glutamic acid (glu), dialanine (diala) and cyanate. P. donghaiense exhibited standard Monod-type growth kinetics over a range of N concentraions (0.5–500 μmol N L⁻¹ for NO₃⁻ and NH₄⁺, 0.5–50 μmol N L⁻¹ for urea, 0.5–100 μmol N L⁻¹ for glu and cyanate, and 0.5–200 μmol N L⁻¹ for diala) for all of the N compounds tested. Cultures grown on glu and urea had the highest maximum growth rates (μ_m, 1.51±0.06 d⁻¹ and 1.50±0.05 d⁻¹, respectively). However, cultures grown on cyanate, NO₃⁻, and NH₄⁺ had lower half saturation constants (K_μ, 0.28–0.51 μmol N L⁻¹). N uptake kinetics were measured in NO₃⁻-deplete and -replete batch cultures of P. donghaiense. In NO₃⁻-deplete batch cultures, P. donghaiense exhibited Michaelis-Menten type uptake kinetics for NO₃⁻, NH₄⁺, urea and algal amino acids; uptake was saturated at or below 50 μmol N L⁻¹. In NO₃⁻-replete batch cultures, NH₄⁺, urea, and algal amino acid uptake kinetics were similar to those measured in NO₃⁻-deplete batch cultures. Together, our results demonstrate that P. donghaiense can grow well on a variety of N sources, and exhibits similar uptake kinetics under both nutrient replete and deplete conditions. This may be an important factor facilitating their growth during bloom initiation and development in N-enriched estuaries where many algae compete for bioavailable N and the nutrient environment changes as a result of algal growth.