Ocean acidification mediates the photosynthetic response to UV radiation and temperature increase in the diatom Phaeodactylum tricornutum.

LI, Y.; GAO, K; VILLAFAÑE, V. E.; HELBLING, E. W.

BIOGEOSCIENCES

COPERNICUS PUBLICATIONS

Lugar: Gottingen; Año: 2012 vol. 9 p. 3931 - 3942

1726-4170

Increasing atmospheric CO2 concentration is re-sponsible for progressive ocean acidification, ocean warm-ing as well as decreased thickness of upper mixing layer (UML), thus exposing phytoplankton cells not only to lower pH and higher temperatures but also to higher levels of solar UV radiation. In order to evaluate the combined effects of ocean acidification, UV radiation and temperature, we used the diatom Phaeodactylum tricornutum as a model organism and examined its physiological performance after grown un-der two CO2 concentrations (390 and 1000 µatm) for more than 20 generations. Compared to the ambient CO2 level (390 µatm), growth at the elevated CO 2 concentration in-creased non-photochemical quenching (NPQ) of cells and partially counteracted the harm to PS II (photosystem II) caused by UV-A and UV-B. Such an effect was less pro-nounced under increased temperature levels. The ratio of repair to UV-B induced damage decreased with increased NPQ, reflecting induction of NPQ when repair dropped be-hind the damage, and it was higher under the ocean acidifi-cation condition, showing that the increased pCO2 and low-ered pH counteracted UV-B induced harm. As for photosyn-thetic carbon fixation rate which increased with increasing temperature from 15 to 25 ◦C, the elevated CO2 and temper-ature levels synergistically interacted to reduce the inhibition caused by UV-B and thus increase the carbon fixation.