Do increased temperature and CO2 levels affect the growth, photosynthesis, and respiration of the marine macroalga Pyropia haitanensis (Rhodophyta)? An experimental study

The marine red macroalgae Pyropia haitanensis (Rhodophyta) were cultured at 18 and 22A degrees C, and at 390 and 1,000 ppm CO2, to examine the potential influence of global change on this commercially important species. The results showed that elevated CO2 or temperature hardly affected the relative growth rate. However, the maximal photochemical yield (F (v)/F (m)) was increased by elevated CO2 or temperature. The light-saturated maximum photosynthetic rates significantly increased with the increasing growth temperature, but decreased dramatically with elevated CO2. While the increasing growth temperature enhanced the dark respiration (R (d)), elevated CO2 had no significant effect on it. An increase of growth temperature lowered the temperature sensitivities (i.e., the Q (10) values) of both gross photosynthesis (P (g)) and respiration, whereas elevated CO2 did not significantly affect the Q (10) values for these two metabolic processes. Algae grown at 22A degrees C exhibited higher ratio of R (d) to P (g) than 18A degrees C-grown algae. By contrast, CO2-enriched growth conditions exerted no significant effect on the ratio. The results suggested that elevated temperature exerted a greater pronounced effect on carbon metabolism than elevated CO2 did. We proposed that the growth of P. haitanensis would not be stimulated by the ongoing climate change (increasing atmospheric CO2 and global warming).