Effects of nitrogen source, N:P ratio and N-pulse concentration and frequency on the growth of Gracilaria cornea (Gracilariales, Rhodophyta) in culture

Abstract

The effects of nitrogen source, nitrogen:phosphorus ratio, nitrogen pulse concentrations and pulse frequency on Gracilaria cornea growth were investigated under laboratory cultures. No significant differences in growth rate were detected between nitrogen sources, the mean growth rate decreased from ca. 14 to 11% d-1 over 8 weeks. Our results indicate that G. cornea can efficiently grow either with inorganic (NH4-N, NO3-N, NO3NH4) or organic (urea) nitrogen. The N:P ratio had a significant effect on G. cornea specific growth rate at 10:1 treatment (8.53% d-1) when compared with ambient phosphate concentration (10:0), which produced the lowest growth rate (2.88% d-1). Neither nitrogen pulse concentration nor pulse frequency showed a significant effect on the specific growth rate, however, pulse frequency significantly affected biomass increase at 50 μM nitrogen (p < 0.05). Nitrogen sources containing NH4-N produced the highest phycoerythrin and protein contents being the most important N storage in G. cornea. The nitrogen storage capacity of G. cornea allows it to grow over a 7 day period with low nitrogen concentrations (< 50 μM). The understanding of nitrogen enrichment in G. cornea cultivation can be applied to manipulate pigment content or agar synthesis, and give the basis for its use in on-land biofiltering systems.