A study of the influence of nitrate supply on intracellular protein and nitrogen components in the kelp Saccharina latissima

Saccharina latissima were cultivated in tanks with three different levels of nitrate supply. The temperature was around 12 to 18 ℃ and salinity was around 24 to 29 during the experiment. Seaweeds cultivated at Medium N concentration (29.0±4.6μg/l) showed the fastest growth rate among the three treatments, and the growth rate of seaweeds at High N concentration (143±13μg/l) was not significantly higher than that at Low N concentration (18.1±1.5μg/l). Seaweeds cultivated at High N concentration showed a significantly higher level of intracellular DIN (0.22±0.02mg/g of dry weight), DON (1.4±0.1mg/g of dry weight), Protein (103.8±1.9mg/g of dry weight), and total-N (2.3±0.1% of dry weight) in the tissue than that grown at Low N and Medium N concentration (p<0.05). The concentration of nitrate in the water for Medium N treatment was 29.0±4.6μg/l, which was significantly higher than that grown in Low N treatment (18.1±1.5μg/l) (p<0.05), but the gap of nitrate level for these two treatments was not big. Seaweeds cultivated at Low N concentration did accordingly not have a significant lower level of DIN (0.05±0.11mg/g of dry weight), DON (0.40±0.08mg/g of dry weight), Protein (80.6±5.1mg/g of dry weight), and total-N (1.4±0.1% of dry weight) in the tissue compare with the seaweeds cultivated at Medium N concentration (p>0.05). Intracellular DIN, DON and protein were positively correlated (p<0.05) to the ambient nitrate concentration during growth.The elemental C/N ratio (weight) ranged from 13.7 mgC·(mgN)-1 for the plants grown in High N concentration (Day 42) to 27.7 mgC·(mgN)-1 in the Low N concentration (Day 62). Overall, at high nitrate supply, plants showed lower C/N ratio. The protein-to-nitrogen conversion factor for High N concentration (4.63±0.32 protein·N-1) was significantly lower than that in Low N concentration (5.78±0.35 protein·N-1) (p