Ultraviolet radiation and temperature effects on photosynthesis and silicate consumption in two marine diatoms

MARCOS G. LAGUNAS; VIRGINIA E. VILLAFAÑE; E. WALTER HELBLING

Portland, Oregon, USA

Congreso; 2010 Ocean Sciences Meeting; 2010

Increases in ultraviolet radiation (UVR, 280-400 nm) at the Earth?s surface and inaverage temperatures are stress factors for phytoplankton. In this study, one-week longexperiments were conducted to assess the combined effects of UVR and temperature oncultures of the two marine diatoms Thalassiosira weissflogii (Grunow) andAsterionellopsis glacialis (Cleve & Moller). Cultures were incubated at two differenttemperatures (i.e., 18 and 23 C) and three radiation treatments: (1) PAB treatment (280-700 nm): UVR + photosynthetically active radiation (PAR); (2) PA treatment (320-700nm): ultraviolet A radiation (UV-A) + PAR, and (3) P treatment (400-700 nm): only toPAR. The photoperiod was 12:12 h light:dark. Samples were taken daily for themeasurement of chlorophyll concentration, cell density, silicate concentration, andphotochemical quantum yield (before and after the illumination period).In both species, and regardless of temperature, cultures under the P treatment grewexponentially for 72 h, while cultures under treatments PA and PAB took a longer periodof time. The silicate consumption in cultures under the PAB treatment was lower thanthat under the PA and P treatments. The photochemical quantum yield showed a similarpattern under the three treatments, with a significant low value at the end of the period ofillumination and a significant high value at the end of the darkness period. In A. glacialis,an increase in temperature from 18 to 23 C caused a shorter exponential grow phase forall treatments and a similar silicate depletion between PA and P treatments. The patternof the photosynthetic quantum yield did not differ in the three treatments. In T.weissflogii, the change from 18 to 23 C led to a negative growth rate in the cultures under the PAB treatment and similar silicate depletion between PAB and PA treatmentswhile depletion under P remained high. The P treatment also showed the lowest values bythe end of the exponential growth at 18 C while it had the highest values during theexperiment at 23 C. The results from this study show species-specific responses to UVRwhen temperature increases by 5 C, and may help understand the ecologicalconsequences of climate change.