Elevated-CO2 and nutrient limitation synergistically reduce the growth and photosynthetic performances of a commercial macroalga Gracilariopsis lemaneiformis

The oceans absorb a large amount of CO2 from the atmosphere, which leads to the increase of ocean acidity. Due to the uncoordinated absorption ratio of N and P in macroalgae cultivation, the nutrients in coastal areas are limited. At present, there are relatively few studies on ocean acidification combined nutrients limitation on commercial macroalgae. This study investigated the economically important red algae Gracilariopsis lemaneiformis, and explored its physiological responses under the combination conditions of ocean acidification and nutrients limitation. In this study, Gracilariopsis lemaneiformis were cultured under two CO2 conditions (400 and 1000 mu atm) and four nutrient conditions (HN, 103.1 mu mol L-1; LN, 3.1 mu mol L-1; HP, 10.1 mu mol L-1; LP, 0.1 mu mol L-1). The results showed that elevated CO2 had no significant effect on G. lemaneiformis growth under P sufficiency (10.1 mu mol L-1) but was significantly reduced under P limitation (0.1 mu mol L-1). Especially under N (3.1 mu mol L-1) and P (0.1 mu mol L-1) limitation, the elevated CO2 had the most significant negative impact on the growth of G. lemaneiformis. Under elevated CO2, P limitation reduced the net photosynthetic rate and relative electron transport rate of G. lemaneiformis. In addition, the dual limitation of LNLP significantly reduced the chlorophyll a content but increased the phycocyanin content under elevated CO2. At low nutrient levels, the elevated CO2 significantly reduced carotenoid, phycoerythrin and soluble protein contents. Our findings suggested that ocean acidification and nutrient limitation synergically inhibited the growth and photosynthetic performances of G. lemaneiformis, and P limitation has a greater effect on G. lemaneiformis. The results can provide valuable information for the seedling field cultivation and selective breeding of G. lemaneiformis in the future.