LAUSR

Atmospheric CO2 concentration is predicted to nearly double by the end of this century. There are a large number of reports on the effects of elevated atmospheric CO2 concentrations on seaweeds. However, the investigation concerning the impacts of combined effects of elevated atmospheric CO2 concentrations and incubation densities on seaweeds is very limited. The marine macroalga Pyropia haitanensis was cultured in jars containing 10 L seawater under outdoor conditions. The treatments were designated as ambient (390 μL·L-1) and elevated (800 μL·L-1) CO2 concentrations, and three incubation densities (1.0, 2.0, and 4.0 g FW·L-1), to examine the effects of elevated CO2 on growth, nutrient uptake percentage, and photosynthesis on the algae grown at different incubation densities conditions. The results showed that elevated CO2 significantly enhanced the relative growth rate (RGR) and nutrient uptake percentage, but inhibited photosynthesis irrespective of the incubation density. The RGR and photosynthesis of P. haitanensis were decreased with increased incubation density. The RGR was even negative at high incubation density of 4.0 g FW·L-1. The nutrient uptake percentage was enhanced with increasing incubation density, regardless of the CO2 concentration in culture. Our results suggested that lower density-grown P. haitanensis was more responsive to CO2 enrichment than higher density-grown algae.