Organic and inorganic nitrogen utilization by nitrogen-stressed cyanobacteria during bloom conditions

• Published in: Journal of applied phycology 2014-02, Vol.26 (1), p.299-309
• Main Authors: Chaffin, Justin D., Bridgeman, Thomas B.
• Format: Article
• Language: English
• Subjects: Amino acids; Ammonium; Biomedical and Life Sciences; Ecology; Eutrophication; Freshwater & Marine Ecology; Lakes; Life Sciences; Microcystis aeruginosa; Nitrates; Nitrogen; Nitrogen enrichment; Planktothrix; Planktothrix agardhii; Plant Physiology; Plant Sciences; Stable isotopes; Urea
• ISSN: 0921-8971; 1573-5176
• DOI: 10.1007/s10811-013-0118-0

Cyanobacterial blooms often occur in lakes that have high phosphorus (P) and low nitrogen (N) concentrations, and the growth rate of the blooms is often constrained by N. For these reasons, many researchers have suggested that regulation of both P and N is required to control eutrophication. However, because N occurs in many bioavailable forms, regulation of a particular form may be beneficial rather than regulation of all N forms. To address how N-stressed cyanobacteria respond to various N inputs, N enrichment experiments (nitrate, ammonium, urea, and alanine) were performed during N-limited cyanobacterial blooms in Maumee and Sandusky Bays of Lake Erie and in Grand Lake St. Marys (GLSM). Bioavailable N (nitrate, urea, and ammonium) concentrations were also determined. Microcystis aeruginosa dominated the Maumee Bay bloom, where the highest growth rates were in response to ammonium additions, and lowest growth rates were in response to nitrate. Urea and the amino acid alanine resulted in intermediate growth rates. Planktothrix agardhii dominated the Sandusky Bay and GLSM blooms, where nitrate, ammonium, and urea addition resulted in similar growth rates. Additions of alanine did not stimulate growth of the Planktothrix blooms. Incubations using stable isotope 15 N showed the cyanobacteria had a preference for ammonium, but the other forms were also assimilated in the presence of ammonium. These results show that cyanobacterial blooms will assimilate multiple forms of N to support growth. Thus, if lake managers do decide that N abatement is necessary, then all forms of bioavailable N need to be constrained.