The carbon fixation and secretion of economic seaweed Gracilariopsis lemaneiformis under high CO2 and nitrate treatment: a CDR solution in aquaculture

Gracilariopsis lemaneiformis is an economic seaweed. It can play critical role in carbon dioxide removal in aquaculture. In this study, we presented physiological and transcriptomic methods to analyzed the response of G. lemaneiformis to high CO2 concentration, especially the carbon fixation and secretion. Overall design: The Gracilariopsis lemaneiformis was collected from the macroalgal farm (119.31 °E, 26.39 °N) in Ningde city, Fujian province of China in April 2023. A detail clean of sediment, fragment and other impurities were performed. The culture medium was coastal seawater obtained from Jinjiang city, Fujian province of China. The seawater was standing for 30 days, preserved in 17°C and filtered by ultrafiltration water purifier with 0.1 µm pore diameter (MUF1580-2T, Midea Group Co., Ltd). Before culturing, the G. lemaneiformis was cultured in nature seawater with two antibiotics (Penicillin, 400 U·mL-1; Streptomycin, 0.4 mg·mL-1) for reducing the bacterial abundance in the two days. After that, the G. lemaneiformis were shifted to new medium for the wipe off of residual antibiotics in another two days. Finally, the G. lemaneiformis was transfer to new medium for 7 days of starvation. The thalli were cultured with 0.5 g·L-1 in 1 L polycarbonate bottle, at the temperature of 17°C, the light tensity of 100 µmol·photons·m-2 s-1 with the light dark cycle of 12 h: 12 h. Moreover, two crossing independent variables (CO2 concentration and nitrate concentration) were set as 4 groups which was put as Table. 1. 50% of culture solution was exchange for fresh filtered seawater with equivalent nutrient and adequate aeration every 4 days. The nutrient was added in each two days.