Variations in photosynthetic characteristics of the Antarctic marine brown algaAscoseira mirabilisin relation to thallus age and size

Abstract

Growth, photosynthesis, dark respiration, chlorophyll a (Chl a) content and dry weight were measured in 2- and 3-year-old plants of Ascoseira mirabilis (Ascoseirales), cultivated in the laboratory under changing daylengths which matched the seasonal variations in the Antarctic. Determinations were made in four thallus regions. Growth of A. mirabilis was seasonal, with higher rates in spring. Parameters such as net photosynthesis (P max), photosynthetic efficiency (α), both measured on a fresh weight (FW) basis, and dry weight content, showed significant age- and size-dependent variations. In contrast, no variations were observed in dark respiration, initial light-saturating point of photosynthesis (I k) and Chl a contents. P max had maximum values close to 16·5 μmol O2 g-1 FW h-1 in 2-year-old plants, whereas in 3-year-old plants maximum values of 8 μmol O2 g-1 FW h-1 were determined. The α-values reached maximum rates of 1.4 and 0.6 μmol O2 g-1 FW h-1 (μmol photons m-2 s-1)-1 in 2- and 3-year-old plants,...