Experimental assessment of UV effects on temperate marine phytoplankton when exposed to variable radiation regimes

BARBIERI, E.S.; VILLAFAÑE, V.E.; HELBLING, E.W.

LIMNOLOGY AND OCEANOGRAPHY

AMER SOC LIMNOLOGY OCEANOGRAPHY

Año: 2002 vol. 47 p. 1648 - 1655

0024-3590

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} @font-face {font-family:Calibri; panose-1:2 15 5 2 2 2 4 3 2 4; mso-font-charset:0; mso-generic-font-family:swiss; mso-font-pitch:variable; mso-font-signature:-1610611985 1073750139 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; text-align:justify; text-indent:9.05pt; line-height:150%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-family:"Times","serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:Calibri; mso-bidi-theme-font:minor-latin; mso-fareast-language:EN-US;} .MsoPapDefault {mso-style-type:export-only; text-align:justify; text-indent:9.05pt; line-height:150%;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Phytoplankton samples were collected at Bahía Engaño, Chubut, Argentina (43ºS, 65ºW) at different times of the year to assess the combined impact of ultraviolet radiation (UVR, 280 – 400 nm) and vertical mixing (i.e., the depth of the upper mixed layer, UML) on photosynthesis.  Samples were exposed to fixed and fluctuating radiation regimes in an illuminated chamber at 15 °C (PAR = 66 W m-2; UV-A = 15.3 W m-2; UV-B = 0.7 W m-2), receiving either PAR+UVR or PAR only.  A comparison between fixed and rotating systems showed that when ZUML / ZEu = 0.6 (i.e., 60% of the euphotic zone was mixed), only post-bloom assemblages (co-dominated by nanoplanktonic flagellates and diatoms - Chaetoceros spp.) were affected significantly by UVR.  Integrated carbon fixation values during pre- and post-bloom periods were higher under mixed conditions than under fixed irradiances.  However, during the bloom (dominated by the microplanktonic diatom Odontella aurita), phytoplankton exposed to fluctuation radiation regimes had lower integrated carbon fixation.  When post-bloom samples were exposed to different mixing conditions, integrated UVR – induced inhibition reduced carbon fixation by 11-13 % when ZUML / ZEu = 0.6, whereas when ZUML / ZEu = 0.91, carbon fixation increased by 7-12  %.  The differences in responses observed between pre-bloom, bloom and post-bloom samples can be attributed to a number of factors, such as the light history of cells, taxonomic composition and size structure of the community and most probably reflect the different inhibition kinetic of these assemblages.