The effect of growth rate, phosphorus concentration, and temperature on N2 fixation, carbon fixation, and nitrogen release in continuous cultures of Trichodesmium IMS101
Limnol. Oceanogr., 50(3), 2005, 839-849 | DOI: 10.4319/lo.2005.50.3.0839
ABSTRACT: With the use of continuous culture systems, rates of dinitrogen (N2) and carbon (C) fixation and nitrogen (N)- and C-based doubling times were assessed in Trichodesmium IMS101 growing exponentially at steady state dilution rates of 0.10, 0.20, and 0.33 d-1 (doubling times of 10, 5, and 3 dwithin the range reported for natural populations). Rates of C fixation, N2 fixation, and N release were examined in replicate culture systems with several techniques. Biomass-specific C uptake varied little with population doubling time, but N2 fixation and N release varied markedly among treatments. Total daily gross N2 fixation rates and estimated N release rates were higher in cultures with higher dilution rates. Cultures grown at lower dilution rates had higher daily C:N2 fixation ratios and lower N release rates. Consistent with other studies, it was estimated that Trichodesmium released about 80-90% of their recently fixed N2 during growth. Turnover of cellular C estimated from carbon fixation was a good estimator of population growth rates in steady state cultures, whereas turnover of cellular N estimated from gross or net N2 fixation was not. Small changes in temperature (24°C vs. 28°C) did not appear to affect gross N2 fixation, whereas inorganic phosphorus (1 vs. 5 µmol L-1) supply had a large effect on N2 fixation. These results suggest that continuous culture systems are excellent for elucidating physiological responses of Trichodesmium under ecologically relevant growth conditions and provide a framework for assessing highly variable field estimates of N2 and C fixation.