Phosphorus-limited growth dynamics in two Baltic Sea cyanobacteria, Nodularia sp. and Aphanizomenon sp.

Abstract

Rates of carbon (C) specific growth and nitrogen (N2) fixation were monitored in cultures of Baltic Sea Nodularia and Aphanizomenon exposed to gradual limitation by inorganic phosphorus (P). Both cyanobacteria responded by decreased cellular P content followed by lowered rates of growth and N2 fixation. C-specific growth and cellular N content changed faster in Aphanizomenon both when inorganic P was lowered as well as during reintroduction of P. Aphanizomenon also showed a more rapid increase in N-specific N2 fixation associated with increased C-specific growth. When ambient concentrations of inorganic P declined, both cyanobacteria displayed higher rates of alkaline phosphatase (APase) activity. Lower substrate half-saturation constants (KM) and higher Vmax : KM ratio of the APase enzyme associated with Nodularia suggest a higher affinity for dissolved organic P (DOP) substrate than Aphanizomenon. Aphanizomenon, which appears more sensitive to changes in ambient dissolved inorganic P, may be adapted to environments with elevated concentrations of P or repeated intrusions of nutrient-rich water. Nodularia on the other hand, with its higher tolerance to increased P starvation may have an ecological advantage in stratified surface waters of the Baltic Sea during periods of low P availability.

Carbon and nitrogen fluxes associated with the cyanobacterium Aphanizomenon sp. in the Baltic Sea

“…Carbon-specific net photosynthesis rates were similar to optimal rates reported using the 14 C method in field-sampled Aphanizomenon from the Baltic Sea (Walve and Larsson, 2007) as well as in cultures of Aphanizomenon isolated from the Baltic Sea in the same area as that of this study (Degerholm et al, 2006). The 14 C method provides an estimate of photosynthesis, which is usually considered to represent a rate between gross and net photosynthesis (that is the net carbon retainment in the cell).…”

Release of fixed N2 and C as dissolved compounds by Trichodesmium erythreum and Nodularia spumigena under the influence of high light and high nutrient (P)

“…Mills et al 2004, Degerholm et al 2006. Our results are insufficient to clearly verify the hypothesis that increases in the supply of limiting nutrients like phosphorus fuel N 2 fixation and thus the release of nitrogenous compounds.…”

Response of <i>Nodularia spumigena</i> to <i>p</i>CO<sub>2</sub> – Part 3: Turnover of phosphorus compounds

“…Calm conditions, a salinity of 7-8, temperatures >16 • C, and a N : P ratio <8 promote the formation of extensive Nodularia blooms in the sea surface layer (Wasmund, 1997). Degerholm et al (2006) suggested that Nodularia sp. is better adapted than Aphanizomenon sp.…”

“…Measurable DOP components include deoxyribonucleic acid (DNA), ribonucleic acid (RNA) (e.g., Karl and Bailiff, 1989), adenosine-5 -triphosphate (ATP) (e.g., Björkman and Karl, 2001), and phospholipids (PL) (e.g., Suzumura andIngall, 2001, 2004). DNA, in addition to its fundamental role in heredity for all self-replicating organisms (Karl and Bailiff, 1989), gained further attention when DeFlaun et al (1987) examined the contribution of its dissolved form to general DOM dynamics. RNA is involved in protein synthesis, which is required for growth (Dortch et al, 1983).…”