Comparative physiological ecology of Bostrychia moritziana (Ceramiales, Rhodophyta) from freshwater and marine habitats

Abstract

The comparative physiological ecology of two freshwater and one marine isolate of Bostrychia moritziana (Sonder ex Kützing) J. Agardh from Venezuela and one marine isolate from Australia was investigated. Growth pattern and the concentrations of the isomeric hexitols d-dulcitol and d-sorbitol were examined in relation to a range of salinities and photon fluence rates. Photosynthesis-irradiance patternswere also investigated. The freshwater isolates from Venezuela and the marine isolate from Australia showed the best growth at 4–5%,while the marine isolate from Venezuela exhibited a broad maximum between 5.3 and 31.8%. All isolates are low-light adapted: one freshwater and one marine isolate from Venezuela displayed strong growth (7–8% d−1) at 12 μmol photons m−2 s−1 with increasing growth rates (12.5% d−1) at 60 μmol m–2 s−1, whereas the Australian isolate exhibited almost the same rate of about 5% d−1 between 1.5 and 60 μmol photons m−2 s−1 and the other freshwater isolate showed a steady growth rate (3.5% d–1) from 12 to 60 μmol m−2 s−1. All isolates exhibited low light compensation points (5.5–14.2 μmol photons m−2 s−1) and low photon fluence rates for saturation of photosynthesis (42.5–87.0 μmolphotons m−2 s−1), indicating that these are typical ‘shade-plants’. In the laboratory the four isolates of B. moritziana produced increasing concentrations of d-dulcitol and d-sorbitol when the salinities were increased. In hypersaline treatment the relative amounts of sorbitol and dulcitol were isolate specific. Field material of both freshwater isolates contained only d-sorbitol whereas laboratory-cultured material contained sorbitol and dulcitol. All data indicate a different physiological response pattern for each isolate, pointing to the evolution of different ecotypes within this species.