Physiological and transcriptomic responses of Saccharina latissima from the Arctic to temperature and salinity stress

The Arctic region is currently facing substantial environmental changes. Melting of glaciers as a consequence of increasing temperature subsequently creates stressful environmental conditions, such as reduced salinity in coastal habitats of kelp beds. We investigated the physiological and transcriptomic performance of the sugar kelp Saccharina latissima from Kongsfjorden (Svalbard, Norway) over a 24-hour exposure at two salinities (20 and 30 psu) after a 7- day pre-acclimation at three temperatures (0, 8 and 15°C). The results demonstrate that the maximum quantum yield of PS II (Fv/Fm) at 15° C was significantly higher than at 0° C, but showed no difference at the two salinities. Pigment content exhibited similar response patterns. Salinity, however, affected gene expression much stronger than temperature. The highest number of differentially expressed genes (DEGs;-DESeq2 with log2Ratio≥2), compared to the control at 8°C and normal salinity, was found in the specimens at 8°C and low salinity (1,374), followed by samples at 0°C and low salinity (1,193). The lowest number of DEGs appeared in the individuals at 0°C and normal salinity (274). Expression profile changes mainly focused on regulations of photosynthetic components and transport processes, as well as induction of ROS scavengers. On the physiological level, our findings indicate a high plastic performance of S. latissima at higher temperatures and lower salinities accompanied by significant gene expression modulatio