Interactive effects of ocean acidification and nitrate on Ulva lactuca

Abstract

The global ocean is undergoing gradual acidification and eutrophication which may have significant impacts on macroalgal communities. However, little is known regarding the interactive effects of ocean acidification (OA) and nitrate on Ulva lactuca, a primary producer widely distributed in coastal waters. This study focuses on the possible interactive effects of OA and elevated nitrate levels on physiological parameters of U. lactuca. Higher nitrate levels may increase growth, photosynthesis, respiration, pigment synthesis, F_v/F_m and Effective Quantum Yield, whereas CO₂ enrichment may result in a reduction in photosynthesis, pigment content, F_v/F_m and Effective Quantum Yield. Higher nitrate levels increase NO₃^- uptake rate and nitrate reductase activity, which are further amplified by elevated CO₂ levels. However, the stimulation of high nitrate towards pigment synthesis and photosynthesis is negatively affected by elevated CO₂ levels. Our results suggest that U. lactuca could potentially increase its biomass in coastal eutrophic waters, and OA in the future is not expected to promote the growth of U. lactuca, but it can enhance its potential biofiltration to remove nitrate from coastal ecosystems.