Growth and Biochemical Responses of Sea Lettuce (Ulva rigida C. Agardh) to Different Nitrogen Sources Under Controlled Culture Conditions

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Özgür Ö., Ak İ.

Aquaculture Studies, cilt.27, sa.1, ss.737-748, 2026 (TRDizin)

Özet

This study evaluated the effects of daily applications of sodium nitrate (NaNO3) and ammonium nitrate (NH4NO3) at different concentrations on the growth, antioxidant activity, phenolic compounds, flavonoids, condensed tannins and pigment contents of the green macroalga Ulva rigida. Under the batch regime, the control received sodium nitrate only at the beginning of each five-day culture cycle, whereas treatment groups received daily nitrogen additions. The highest specific growth rate was recorded in the NO3-3 group (3.84±0.32% day-1), whereas the lowest value was observed in NH4-5 (−0.70±0.14% day-1) (P<0.05). The DPPH inhibition activity ranged from 17.72±2.87% (NO3-4) to 41.10±1.73% (NO3-3). The lowest IC50 value was also determined in NO3-3 (8.65±0.48 mg g-1 ext) (P<0.05). Total phenolic, flavonoid and condensed tannin contents ranged from 0.80±0.10 to 2.35±0.08 mg GAE g-1 ext, 1.64±0.06 to 3.05±0.04 mg RE g-1 ext and 66.72±2.22 to 125.61±0.74 µg CE g-1 ext, respectively (P<0.05). Chlorophyll a and total carotenoid contents were highest in the control group, whereas chlorophyll b was highest in the NO3-5. Correlation analysis and PCA supported differences among nitrogen treatments. These results showed that nitrogen source and application regime affected the growth, antioxidant activity and biochemical characteristics of U. rigida.