Recently there has been a rapid increase in interest regarding the CO2 removal capacity of seaweed, leading to a focus on photosynthesis research. Because direct measuring the dissolved inorganic carbon (CT) uptake rate is challenging, the use of the photosynthetic quotient (PQ), which converts oxygen evolution to carbon fixation, has proven effective. However, PQ is highly sensitive to various environmental factors, including climate change (warming and acidification). This study aimed to investigate the impact of climate change conditions on the PQ of Ulva ohnoi, namely, control (CONT: 271 µatm CO2 & 20°C), acidification (OA: 526 µatm CO2 & 20°C), warming (OW: 307 µatm CO2 & 25°C), and greenhouse (GR: 634 µatm CO2 & 25°C). The PQ was determined through an incubation experiment, where simultaneous measurements of O2 evolution and CT uptake rates were conducted in a seawater medium. The average PQ values were consistently above 1 across all treatments, with the highest PQ values observed in the CONT (1.67 ± 0.03) and the lowest in the OW (1.16 ± 0.04). While increased CO2 levels and light intensity did not affect the PQ value, higher temperatures had a significant impact on the PQ of U. ohnoi. Consequently, it can be expected that increased temperatures will lead to a decrease in PQ, resulting in increased CT uptake compared to O2 evolution. Estimating CT uptake based on O2 evolution may, therefore, lead to an overestimation of the CT uptake rate when applying theoretical PQ.
Kang E. J., Ryu B. D., Kim Y. S. & Kim J. H., 2024. The photosynthetic quotient (PQ) of Ulva ohnoi (Chlorophyta) under future ocean conditions. Journal of Applied Phycology. Article.
