Increase in photosynthetic efficiency as a strategy of planktonic organisms exploiting deep lake layers.

MODENUTTI, BEATRIZ E; ESTEBAN GABRIEL BALSEIRO, ESTEBAN G. BALSEIRO, BALSEIRO, E.G; CALLIERI, C.; QUEIMALINOS, CLAUDIA P; BERTONI, R.

FRESHWATER BIOLOGY (PRINT)

Blackwell Publishing

Año: 2004 vol. 49 p. 160 - 169

0046-5070

1. The photosynthetic efficiencies of the mixotrophic ciliate Ophrydium naumanni and theautotrophic dinoflagellate Gymnodinium paradoxum were investigated using laboratory andfield experiments in Lake Moreno Oeste (41
5¢S and 71
33¢W, 758 m a.s.l.), in the NahuelHuapi System (North Patagonia, Argentina).2. The effect of different underwater light intensities on net primary production (NPP) wasassessed during one summer. Additionally, laboratory experiments were carried out toobtain photosynthesis-irradiance response curves for each species.3. Ophrydium naumanni and G. paradoxum dominated the metalimnetic (30 m depth) deepchlorophyll maximum (DCM) in the lake.4. Despite these deep higher abundances, the cell-specific production of both species washigher at 10 m than at 30 m (DCM) depth. In addition, at 5 m depth, NPP was reduced byPAR + UV-A radiation.5. Both species exhibited a positive NPP at very low irradiance but the mixotrophic ciliatewas more efficient in exploiting the DCM irradiance level both in situ and at comparablelight intensities in laboratory experiments. Light acclimatised O. naumanni showed ahigher NPP at lower irradiances and photoinhibition at medium and high irradiances.6. Under the strong wind-driven turbulence commonly found in Patagonian lakes,organisms cannot select their position in the epilimnetic water column and will be draggedto potentially harmful UV radiation levels. Thus, metalimnetic DCM colonisation by thesetwo species represents a tradeoff between higher survival and lower cell-specific NPP.