Steiner, Niko; Nilsen, Anne M; Gauci, Clément; Jueterbock, Alexander; Bartsch, Inka: Heat stress response of Saccharina latissima sporophytes of different age classes to gametophyte and sporophyte priming - 3 [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.996550 (dataset in review)

We assessed the heat tolerance of microscopic, juvenile and adult sporophytes under heat stress and in response to gametophyte or sporophyte priming in five experiments. Experiment 1: we primed Saccharina latissima gametophytes (Lofoten 2023; 15°C clonal culture; n = 7) for 3 weeks at 0°C, 10°C, and 20°C and induced gametogenesis at 10°C for 2 weeks. Resulting microscopic sporophytes were subjected to a 14-day heat stress treatment at 20°C, 21.5°C, and 23°C, where we counted the number of alive and dead sporophytes and calculated the survival rates. Experiment 2: sporophytes were cultivated after gametogenesis for an additional 4 weeks before we subjected them to a 14-day simulated heat wave (13°C for 3 days, 16°C for 2 days, 18°C for 2 days, 20°C, 21°C and 22°C for 1 day each, 23°C and 24°C for 4 days each, and recovery at 20°C for 7 days), during which we assessed the photosynthetic performance by measuring quantum yield (Fv/Fm). Sporophytes that survived the heat wave were cultivated at 15°C for 64 days to recover, after which we measured their size (length and blade area). Experiment 3: primed (0°C, 10°C, 20°C; 3 weeks) gametophytes (Lofoten 2023; 10°C mixed culture; n = 5) were sown on ropes and reared in a mariculture experiment (2 months hatchery, 4 months mariculture). Adult sporophytes were sampled and exposed to the same 14-day heat stress treatment at 20°C, 21.5°C, 23°C with a 10°C control group. We measured growth (length and blade area), Fv/Fm, and the percentage of healthy area (as % blade area with Fv/Fm > 0.6). Experiment 4: sporophytes from the 0°C gametophyte priming treatment of the same mariculture experiment recovered at 10°C for 24 days. Meristematic discs were exposed to a 1-day sporophyte priming trigger (T). A control group (C) remained at 10°C. After 3 days recovery at 10°C both groups were subjected to a 7-day heat stress treatment at 20°C, 21.5°C, 23°C, and 25°C, where we measured growth (disc area) and Fv/Fm. Experiment 5: gametogenesis of gametophytes (Spitsbergen 2011, 2015; 5°C clonal culture, n = 5) was induced at 5°C and sporophytes reared for 6 months. Sporophytes were distributed to three treatment groups. A 17-day heat wave (from 5°C to 20°C and back) followed by a 1-day priming trigger at 21.5°C (HWT); 17 days at 10°C and a 1-day priming trigger (T); a control remaining at 10°C throughout (C). All groups were subjected to a 7-day heat stress treatment at 20°C, 21.5°C, 23°C, and 25°C, where we measured Fv/Fm, percentage of healthy area and survival. All laboratory experiments were carried out at the Alfred Wegener Institute in Bremerhaven, from January to July 2024. The mariculture experiment took place at the hatchery of Polaralge AS (Sandhornøy, Norway; December - February 2024) and the deployment site of Lofoten Blue Harvest (Lilje Engla, Lofoten, Norway; 68°16'02.8N 15°06'14.8E; February – June 2024).