Production and biomass of picophytoplankton and larger autotrophs in Andean ultraoligotrophic lakes: differences in light harvesting efficiency in deep layers.

CRISTIANA CALLIERI,; BEATRIZ ESTELA MODENUTTI O BEATRIZ MODENUTTI O B. MODENUTTI; P QUEIMALINOS, CLAUDIA; ROBERTO BERTONI,; E BALSEIRO,

Aquatic Ecology

Springer

Lugar: Holanda; Año: 2007 vol. 41 p. 511 - 523

1386-2588

We measured biomass and primary productionof picophytoplankton (PicoPhy: 0.2?2 mm)and of autotrophic size fraction >2 mm in six deepultraoligotrophic lakes in the Andean-Patagonianregion (around 41S) during summer stratification.Surface Photosynthetically Active Radiation (PAR)ranged from 1277 to 1849 mmol photons m
2 s
1,and the euphotic zone, generally deeper than themixed layer, varied between 28 m and 49 m. Wefound a strong photoinhibiting effect of high PARand UV-A at surface levels, whereas UV-B radiation(<320 nm) had low extra contribution in the photosynthesisinhibition. As a consequence, cell numbers,Chl a and primary production rates of both fractionsincreased towards deep layers in all lakes. Thephotosynthetic efficiency (Chl-specific productionper photon unit) of both fractions increased withdepth, although this increase was higher in PicoPhy,indicating a higher fitness to low-light. The per centcontribution of PicoPhy production to total production,showed an inverse significant relation with totaldissolved phosphorus (TDP). Moreover our datafitted the existing database showing a significanttrend towards a decrease of PicoPhy biomass and anincrease of its relative contribution to total biomasswith decreasing trophic state. At very low-phosphorusconcentration, typical of north Patagonian lakes,we found good evidence of the competitive advantageof PicoPhy. Low-light and low TDP may interactto create the most favourable conditions for thesmaller photosynthetic organisms. In conclusion, wefound that at low-light and very low nutrient regimePicoPhy achieves higher photosynthetic efficiencythan the larger autotrophic organisms.