Abstract:To investigate the effect of nitrogen sources (NO3-N, NH4+-N, and Urea) on the physiological characteristics of Sargassum hemiphyllum seedlings, the seedlings were cultured for 24 days in different concentrations of each nitrogen (N) source, and the growth rate and biochemical composition were determined. The results showed that the N source and N concentration had significant effects on the growth rate and biochemical composition of the seedlings. With increasing N concentrations, the relative growth rates and tissue N contents of the seedlings increased, and when tissue N contents approached or reached N requirement (0.032%/d) for the maximum growth rate in 25~150 μmol/L, the relative growth rates reached the maximum at 50 μmol/L. The maximum relative growth rate under Urea enrichment was significantly lower than that under NO3-N and NH4+-N enrichments. The relative growth rate of the seedlings in 10 and 25 μmol/L NH4+-N was significantly higher than that in the same concentration of NO3-N, but the relative growth rate in 50~150 μmol/L showed an opposite change. Except for the highest N concentration (150 μmol/L), the photosynthetic pigments, soluble protein, and tissue nitrogen contents gradually increased, while the soluble sugar content gradually reduced as N concentration increased. At the same N concentration, the contents of soluble sugars, chlorophyll a, and chlorophyll c of seedlings were the highest under NO3-N enrichment, the contents of the soluble protein content and tissue N content were the highest under NH4+-N, and the fucoxanthin content was the highest in Urea-enriched culture medium. When the NH4+-N concentration reached 150 μmol/L, a significant decrease in growth and soluble protein content was observed, indicating the presence of a stressful condition. In conclusion, culture medium enriched in NO3-N (50~150 μmol/L) or NH4+-N (25~100 μmol/L) promoted the growth, photosynthesis, and dry-matter accumulation of S. hemiphyllum seedlings, suggesting that the seedlings may be successfully cultured indoors during summer.
