Photosynthesis, dark respiration and pigment contents of gametophytes and sporophytes of the Antarctic brown alga Desmarestia menziesii

Photosynthetic performance, dark respiration, pigment concentration and fresh : dry weight ratios were measured in different life history stages of the Antarctic brown alga Desmarestia menziesii J. Agardh cultivated under simulated Antarctic conditions. Small gametophytes had the highest pigment concentrations, especially Chl a (1.6 mg g(-1) FW), fucoxanthin (0.8 mg g(-1) FW) and beta-carotene (0.04 mg g(-1) FW). Young sporophytes had the highest Chl c values (0.4 mg g(-1) FW) and high Chl a contents 1.0 mg g(-1) FW). In general, adult reproductive plants contained the lowest pigment concentrations. Net photosynthetic rates (P-max), on a fresh weight basis, were significantly higher in gametophytes (20 mu m O-2 g(-1) FW h(-1)), however, when normalized to Chl a, P-max was higher in adult reproductive plants (24 mu mol O-2 mg(-1) Chl a h(-1)). Dark respiration and photosynthetic efficiency (alpha), calculated both on a fresh weight and Chl a, basis, were considerably higher in the early developmental stages, i.e. gametophytes and young sporophytes. Differences in the light saturation parameter I-k were also found with adult plants having higher values (> 30 mu mol photons m(-2) s(-1)). Dry : fresh weight ratios of adult sporophytes were approximately twice those of gametophytes and young sporophytes. These results indicate that small gametophytes and young sporophytes have shade adapted plant characteristics including high pigment content, high alpha-values, low I-k values and low Chl a-based P-max. These photobiological attributes are related to thallus structure in both phases, and to seasonal reproductive strategy of the species: the different photosynthetic characteristics of gametophytes and young sporophytes, which are formed in winter/spring, and macrothalli, which occur in spring-summer, allows D. menziesii to optimize photosynthetic performance under the strongly seasonal Antarctic light regime.