Phytoplankton photosynthesis in temperate marine ecosystems as affected by ultraviolet radiation and vertical mixing

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

Chicago – Illinois – USA.

Congreso; Twenty-Ninth Annual Meeting of the American Society for Photobiology; 2001

&lt;!-- /* 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-fareast-font-family:Calibri; mso-bidi-font-family:"Times New Roman"; mso-fareast-language:EN-US;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt; mso-ascii-font-family:Calibri; mso-fareast-font-family:Calibri; mso-hansi-font-family:Calibri;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --&gt; This study was carried out to determine the effects of ultraviolet radiation (UVR, 280-400 nm) and vertical mixing on marine phytoplankton photosynthesis.  Samples were collected at Bahía Engaño (43ºS, 65ºW), Patagonia (Argentina) during 2000 from the upper mixed layer (UML), inoculated with radiocarbon and incubated in an illuminated chamber (PAR = 66W•m-2; UV-A = 15.3W•m-2; UV-B = 0.7W•m-2) at 15 °C.  Three different radiation treatments were implemented: PAR only, 400-700 nm (quartz tubes covered with Plexiglas UF-3), PAR+UV-A, 320-700 nm (quartz tubes covered with Mylar-D), and PAR+UVR, 280-700 nm (quartz tubes without filters).  Vertical movement (i.e., change in irradiance) and mixing within the euphotic zone (Eu) were simulated using a moving system in combination with neutral density screens, and compared with a fixed system (i.e., constant irradiances).  Our data indicate that species adapted at low irradiance levels (i. e. Winter samples, generally dominated by microplankton) were more sensitive to vertical mixing than Summer samples (i.e., dominated by nanoplankton), which were acclimated to high irradiance conditions.  With simulated shallow UMLs (UML/Eu <0.5) vertical mixing enhanced the inhibition by UVR.  However integrated production, in a deep simulated UML (UML/Eu > 0.7), was significantly lower when the phytoplankton was mixed vertically, as compared to a “fixed” system.  In this case, removal of UVR caused an additional decrease in the integrated production, and phytoplankton had the capacity to use UV-A to photosynthesize when PAR was relatively low or when the UML was deep.  This work was supported by ANPCyT (PICT97 - 07-00000-02206), Fundación Antorchas (A-13622/1-100), TWAS (98-036 RG/BIO/LA) and Fundación Playa Unión.