Photosynthetic response of Arctic kelp zoospores exposed to radiation and thermal stress

Abstract

Zoospores of Arctic kelp species, Alaria esculenta, Laminaria digitata and Saccharina latissima were exposed to different temperature (2 degrees C to 19 degrees C) and radiation (photosynthetically active radiation (PAR=P), PAR+UV-A (PA), and PAR+UV-A+UV-B (PAB)) conditions in the laboratory. Species-specific responses to the combined effect of light and temperature stress showed sensitivity in the order S. latissima>L. digitata>A. esculenta. The optimum temperature range for photosynthesis in different Arctic kelp species' zoospores was between 7-13 degrees C, temperatures higher than in the natural environment. Short-term response to increasing temperature was non-lethal while moderate temperature increase had an ameliorating effect on the overall biological effect of UVR; where the lowest photoinhibition was observed at 13 degrees C under PAB and higher photosynthetic recovery was observed in UVR-pre-exposed zoospores at 7-13 degrees C compared to 2 degrees C. Above the temperature optima, continued cultivation under high temperature had a negative impact on the recovery of photoinhibition. The higher capacity for non-photochemical quenching (NPQ) in A. esculenta and L. digitata helped to regulate and protect photosynthesis under light and temperature stress compared to S. latissima. The investigated Arctic kelp species may be able to locally survive under the influence of UVR at a certain range of temperature increase but the southernmost distribution range of the species may shift to higher latitudes; although natural selection may result in genotypes adapted to stressful environment.