PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Effect of external pH on growth and photosynthesis of Chlamydomonas sp. isolated from an acidic mining lake, Germany (ph 2.65). Antje Gerloff-Elias^*,1, Elly Spijkerman¹, ¹ University of Potsdam, Institute of Biology and Biochemistry; Maulbeerallee 2, Potsdam, Germany

ABSTRACT- Phytoplankton species living in acidic mining lakes are faced with extreme environmental conditions, such as low pH (2.3-3.5) and high heavy metal concentrations (Fe, Mn, Zn). As a consequence, only specialists, who might well face increased metabolic costs, are able to survive. Previous field studies showed relatively low primary productivity compared to bacterial productivity (Kamjunke, in press.) which support costs attributed to living in such lakes. To study these possible costs further, experiments were performed with the dominant phytoplankton species, Chlamydomonas sp., in a range of external pH conditions. In addition to the measurement of growth, photosynthesis and respiration rates, electron transport capacities of Photosystem (PS) 1 and 2 and P700 re-reduction were also analyzed. Growth and photosynthesis in Chlamydomonas sp. were optimal at pH 3 and 5, underlining its acidophilic nature. Furthermore, these growth and photosynthetic rates at optimum pH were highly comparable to rates of the mesophilic C. reinhardtii. Therefore, life at this species' optimum pH conditions does not seem to bring about large metabolic costs. At both high and low pH, increased non photochemical quenching and increased dark respiration rates were detected together with increased cyclic electron transport around PS 1. Results are discussed in the framework of acclimation to pH stress in relation to proton defense mechanisms, light acclimation and photosystem stochiometry.

KEY WORDS: Chlamydomonas, stress, extreme environment, acidophil