Trentepohlia sp., a terrestrial chlorophyte growing on galvanised iron lamp posts

Abstract

ABSTRACT The common green alga Trentepohlia sp. was found growing as a biofilm on galvanised iron lamp posts where it was exposed to high zinc levels and periodic desiccation. Its sole water sources were rainfall and dewfall. Photosynthesis studies using PAM techniques showed that the alga was a shade-adapted species with a very low optimum irradiance (Eopt) of about 90 μmol photons m−2 s−1, and ETRmax about 80 μmol e− g−1 chlorophyll-a s−1. But, within minutes, it recovered from desiccation (homiochlorophyllous). The alga has a high chlorophyll-b/a ratio (0.470 ± 0.016) and conspicuous chlorophyll-b absorption in vivo, but no measureable Zn-chlorophyll derivatives were found spectrophotometrically. Mannitol experiments using up to 1.5 Osmol kg−1 showed that photosynthesis in Trentepohlia sp. was highly resistant to water stress. Photosynthesis of Trentepohlia sp. was unaffected by pH even though the abundance of CO2 in the experimental medium dropped from 477 mmol m−3 at pH 5 to less than 1 mmol m−3 at pH 9. Thus, Trentepohlia sp. can use both CO2 and HCO3 − as inorganic carbon sources. Acid pH (pH 5) did not increase toxicity of Zn. Trentepohlia sp. was resistant to added Zn with little effect on photosynthetic parameters even at 30 mol m−3 Zn.