Effects of concentrations and ratios of nitrogen and phosphorus on the growth and agar content of Gracilaria lemaneiformis(Rhodophyta)

The effects of concentration and ratio of nitrogen and phosphorus on the growth rate(SGR) and agar content(AC) of red macroalgae Gracilaria lemaneiformis were studied. Results show that nitrate and ammonium, the major nutrient pollutants, have similar effect on the SGR and AC of G. lemaneiformis. Within the tested range of nitrogen concentraion(ammonium-nitrogen 0～50 μmol/L; nitrate-nitrogen 0～100 μmol/L), the SGR increases whereas AC decreases with the increase of nitrogen concentration. The effects of ambient phosphorus and nitrogen on SGR of G. lemaneiformis are similar, but opposite on AC. Different ratios of nitrogen and phosphorus (N∶P ratio) have large influence on the SGR and AC of G. lemaneiformis. SGR of G. lemaneiformis is the highest when it is cultured in 10∶1 ratio among the 1∶1, 10∶1 and 100∶1 treatments; and AC of G. lemaneiformis is the highest in the 1∶1 treatment. Prior to harvest, G. lemaneiformis should be cultured for two weeks in low N∶P ratio and high phosphorus concentration environment to increase the agar content and quality.