Comparison of photosynthetic responses in diploid and haploid life cycle phases of Emiliania huxleyi (Prymnesiophyceae)

TitreComparison of photosynthetic responses in diploid and haploid life cycle phases of Emiliania huxleyi (Prymnesiophyceae)
Type de publicationJournal Article
Year of Publication2005
AuteursHoudan, A, Probert, I, Van Lenning, K, Lefebvre, S
JournalMarine Ecology Progress series

Emiliania huxleyi is a ubiquitous coccolithophore, capable of forming large blooms. This species presents a digenetic heteromorphic life cycle, the non-motile diploid phase typically bearing coccoliths and the flagellated haploid phase being non-calcified. Oxygen production rates at different irradiances of both phases were studied in mid-exponential and transitional growth phases in cultures grown under identical conditions. There were no significant differences in basic photosynthetic parameters ($\alpha$chl a , maximum light utilization coefficient; Pchl amax, the light-saturated maximal rate of photosynthesis; Ek, the light-saturation parameter) between the 2 life-cycle phases; however, whereas the diploid phase did not exhibit photoinhibition at irradiances up to 1000 µmol photons m–2 s–1, photoinhibition was recorded in the haploid phase above 400 to 500 µmol photons m–2 s–1 and photosynthetic rate decreased to ca. 75% of Pmax at 1400 µmol photons m–2 s–1. The 2 phases cultured under identical (non-saturating in terms of light) conditions did not present any significant differences in pigment content. These results are discussed in an ecological context. The lack of photoinhibition could confer a competitive advantage on the diploid stage, notably in a turbulent environment. For the haploid stage, the occurrence of photoinhibition may indicate niche separation (spatial and/or temporal) relative to the diploid phase.