Diversity and photosynthetic traits of picocyanobacteria assemblages in ultraoligotrophic Andean lakes.

CRISTIANA CALLIERI; CARAVATI, E.; MODENUTTI, B.; CORNO, C.,; BALSEIRO, E.; ROBERTO BERTONI

Parma Italia

Congreso; SITE 2008; 2008

AIOL

We investigated the relationships among the Operational Taxonomic Units (OTUs) and the photosynthetic characteristics of picocyanobacteria (Pcy) assemblages in six ultraoligotrophic North Patagonian lakes. Pcy are here the dominant picophytoplankters forming a Deep Chlorophyll Maximum (DPM) at 1 % of surface Photosynthetic Active Radiation (PAR). Automated rRNA intergenic spacer analysis (ARISA) was used for the first time to study the Pcy community composition in freshwaters. The six lakes clustered into two main groups mirroring their history after the Last Glacial Maximum. About 50 % of significant ARISA fragments appeared to be site specific. Others displayed cosmopolitan distribution among lakes as in the case of the OTU 1094, which occurred in all samples and comprised 21 to 95 % of the total amplified DNA. Theoccurrence of specific OTU is related to a peculiar in situ photosynthetic performance of the Pcy community. OTU 738 was significantly related to the chlorophyll specific production. The variation of the photosynthetic traits of the two clusters characterized by different OTU diversity is consistent with the hypothesis that the ITS sequence of Pcy define functionally differentiated groups. The similar Pcy composition in the water column suggests their great acclimation ability.