Effect of photon irradiance and photoperiod on young sporophytes of four species of the Laminariales

Abstract

Four kelp species (Alaria esculenta, Laminaria digitata, L. hyperborea and L. saccharina) were cultured in the laboratory and pretreated so that gametophytes became mature and sporophytes were produced. Young sporophytes less than 3 weeks old were exposed to various light conditions and their survival or relative growth rate in length (RL), and width (Rw) in one experiment, determined. Sporophytes of L. digitata survived poorly in the dark compared with L hyperborea. The minimum photon irradiance allowing growth in L. hyperborea was about 1 #moI m -2 s-I; I-2 #mol m 2 s-Z sustained growth in all the species. The growth of all four species was saturated at 20-30/*mol m z s i of continuous photon irradiance. In shorter daylengths the growth rate was lower both below and above light saturation. Above saturation the growth was considerably faster than would be expected if no photosynthetic products were carried over from the light to the dark period. There was evidence that 2-3 times as much light was necessary to saturate photosynthesis as to saturate growth. Although there were significant differences between the species in R L during the first 10 days, differences in R w and in sporophyte age made it impossible to distinguish fast-or slow-growing species during the first 3 weeks. Single-dimension growth measurements at this developmental stage can thus be misleading. Young sporophytes of L. digitata were more tolerant of strong sunlight than those of L. hyperborea, but in both the survival was higher following acclimation to higher irradiance.

Growth and DNA damage in young Laminaria sporophytes exposed to ultraviolet radiation: implication for depth zonation of kelps on Helgoland (North Sea)

“…was able to sustain growth in culture (Han and Kain 1996). At 18 lmol photon m À2 s À1 in this study, maximum growth rate in L. digitata (1500-2100 h, 0.57±0.17% h À1 ) is comparable to the previous online growth measurements of Lu¨ning (1994) on the same species from Helgoland reported at 0.5% h…”

Influence of ultraviolet-radiation on chlorophyll fluorescence and growth in different life-history stages of three species of Laminaria (phaeophyta)

“…It seems unlikely, therefore, that the responses of the different species to UV-radiation could have a role in determining the natural distribution of the species in the field. A similar conclusion was reached by Kain (1966) and Han and Kain (1996) after comparing the photosynthetic and growth responses of the same three species to different irradiances of visible light, and the zonation of these species in the field (L. hyperborea typically occupies greater depths in the sublittoral zone at Helgoland than L. digitata and L. saccharina; Liining 1970) appears to be unrelated to their photophysiological characteristics, at least as determined in laboratory experiments. However, Liining (1980) observed that gametophytes of L. saccharina could survive longer exposures to winter sunlight than L. digitata or L. hyperborea, and suggested that this could explain the appearance of young sporophytes of L. saccharina relatively high on the shore in early spring.…”

“…The results obtained here indicate that 2 h of exposure to UV-radiation at irradiances slightly lower than those in full sunlight at Helgoland (see "Material and methods -UV-irradiation conditions") inhibits germination and growth of gametophytes; this implies that the establishment and growth of gametophytes could be impaired at the upper limit of the sublittoral zone. However, previous experiments have shown that 15 to 30 min of exposure to direct sunlight is sufficient to kill gametophytes of all three species of Laminaria (Liining 1980) and the young sporophytes of L. digitata and L. hyperborea (Han and Kain 1996). This suggests that UV-radiation combined with high PAR in natural sunlight is more damaging than UV-radiation alone, and that the ecological significance of UV-radiation for macroalgae can be addressed only by conducting experiments in natural radiation.…”

Growth kinetics related to physiological parameters in young Saccorhiza dermatodea and Alaria esculenta sporophytes exposed to UV radiation

“…1) at 16:8 h light-dark photoperiod. An increase in growth rates to longer photoperiod was previously reported in A. esculenta from the British Isles (Han and Kain 1996).…”