Preliminary comparison of atmospheric CO2 enhancement to photosynthesis of Pyropia yezoensis (Bangiales, Rhodophyta) leafy thalli and filamentous thalli

Abstract

SUMMARYIntertidal macroalgae are submerged in seawater at high tide and exposed to air at low tide. When they are exposed to the air, CO2 is the main inorganic carbon source. In this study, the photosynthetic performances of PSI and PSII were measured in different generations of Pyropia yezoensis (leafy thalli and filamentous thalli) that had been exposed to air containing different CO2 concentrations. Changes in photosynthesis during dehydration and salt treatment under the different CO2 concentrations were also analyzed. The results showed that in leafy thalli, the effective photochemical quantum yield of PSII (YII) was enhanced as CO2 increased, which suggested that CO2 assimilation was enhanced and that they can utilize CO2 in the air directly, even when they are subjected to moderate stress. These findings could explain why, in P. yezoensis aquaculture, moderate exposure to air does not lead to a decrease in crop yield. However, in filamentous thalli, there were no significant differences in YII at the CO2 concentrations tested. The expression of genes involved in the Calvin cycle in leafy thalli was higher than that in filamentous thalli. CO2 uptake and biomass of P. yezoensis leafy thalli is larger than filamentous thalli, which may be due to its different carbon utilization mechanism and the adaptation of intertidal environment in the evolutionary process.