Due to the effective removal of phosphorus during eutrophication control and intensive macroalgal cultivation, phosphorus limitation in coastal waters is normalized. As an economic macroalga cultivated on a large scale in production, Gracilariopsis lemaneiformis is also inevitably influenced by the combination of phosphorus limitation, ocean acidification caused by the increase of dissolved CO2 concentration and salinity decrease as a consequence of rainfall. In this study, G. lemaneiformis was cultured for 15 days under two pCO2 levels (LC: 400 μatm, HC: 1000 μatm), two salinities (LS: 22, HS: 30) and two phosphorus concentrations (LP: 0.1 μmol L−1, HP: 10.1 μmol L−1) to study the growth and photophysiology responses of this macroalga to the coupling of phosphorus limitation, ocean acidification and low salinity. Lower phosphorus (LP) treatment substantially reduced multiple parameters compared to higher phosphorus (HP) condition, including relative growth rate (RGR), photosynthetic rate, chlorophyll fluorescence parameters, and the contents of pigments, soluble protein, and soluble carbohydrate. Elevated CO₂ (HC) exposure induced a significant reduction in algal RGR under LP condition, while demonstrating no statistically significant impact on RGR under HP condition. Furthermore, HC treatment significantly inhibited carotenoid biosynthesis under LP condition. Notably, lower salinity (LS) stimulation significantly enhanced RGR in the ambient CO₂ (LC) group, but this promotive effect was completely negated under HC condition. These findings demonstrated that phosphorus limitation had an adverse outcome on algal growth, and phosphorus limitation exacerbated the adverse effect of ocean acidification on its growth. Moreover, the promotion effect of low salinity on algal growth could be neutralized by ocean acidification. This study provided important information about the influence of environmental changes on the photophysiological characteristics of G. lemaneiformis and new breeding directions for large-scale cultivation of coastal economic macroalgae.
Wang J., Wu H., Jia L., Xu J., Chen Z., Lu W., Cen Y. & Zhou W., in press. Ocean acidification interacts with low salinity and phosphorus limitation to modulate growth, photosynthesis, and physiology of mass-cultivated Gracilariopsis lemaneiformis. Journal of Applied Phycology. Article.
