Effect of elevated CO₂ and temperature on Ulva lactuca growth and biochemistry under variable nitrogen levels: predicting future conditions of edible seaweed farming through land-based cultivation system

Marine seaweeds occupy unique ecological niches, and they often compete for essential environmental resources for their survival. As CO₂, temperature and nutrient levels continue to rise globally, this competition is expected to intensify, posing challenges for the coexistence of algae and native species in marine ecosystems. The impacts of stress-causing agents on the physiological performance of algae remain largely understudied. Hence, the focus of the study was to evaluate the interactive response among CO₂ (400 ppm and 1000 ppm), temperature (20 °C and 24 °C) and nitrate (5 µmol/l and 150 µmol/l) with six (1-CC: CT: CN, 2-CC: FT: CN, 3-CC: FT: FN, 4-FC: CT: CN, 5-FC: FT: CN, 6-FC: FT: FN) different combinations (current CO₂ (CC):current temperature (CT):current nitrogen (CN):future temperature (FT):future nitrogen (FN), future CO₂ (FC) on the green seaweed Ulva lactuca through tank cultivation system. The results showed higher growth rate (35.85 ± 2.85%/day) (P < 0.01) in FC:FT:FN, pigments (chlorophyll (Chl) a, 126.98 ± 7.29 mg/g fresh weight (fw); Chl b, 162.91 ± 15.05 mg/g fw; total Chl, 289.79 ± 22.33 mg/g fw) in CC:FT:CN (P < 0.01) and nutritional compositions (protein, 26.12 ± 0.30% of dry weight (dw); carbohydrate, 79.97 ± 2.77% of dw; lipid, 3.0 ± 0.069% of dw) in FC:CT:CN (P < 0.01) combinations. The interactive effect of carbon dioxide, temperature and nitrogen (CTN) on U. lactuca shows that the elevated parameters are individually or in combination significantly enhanced in terms of growth rate (CO₂, temperature, nitrate), pigments (temperature) and nutritional compositions (CO₂). The reported data clearly depicts the vision of noteworthiness of the study among the interactive effects of environmental parameters because of climatic variations excreting influence of seaweed farming.