Fluorescence parameters of White Sea phytoplankton under different nitrogen sources

We investigated dependence of fluorescence parameters and phytoplankton biomass on the nitrogen source and irradiance in enriched flask studies with White Sea plankton from August-September 2007. Phytoplankton was exposed in situ for 18 d with addition of 180 μM/L of nitrogen in the forms of nitrate, urea, ammonia, and glycine under two levels of irradiance. Maximum quantum efficiency of PS2 (Fv/Fm) was determined in the samples adapted to darkness. Rapid light curves were obtained for each sample with the sequential increase of light intensity (8 levels). The maximal relative electron transport rate (rETRmax), the maximum light utilization coefficient (α), and the nonphotochemical quenching (NPQ) were calculated. The phytoplankton abundance increased on nitrogen addition, and the photosynthetic parameters changed. The values Fv/Fm reached 0. 64-0. 71, which indicated a good physiological state of algae and lack of nitrogen limitation. The dynamics of rETRmax and NPQ depended of the nitrogen source and irradiance, while α did not depend on nitrogen addition. © 2013 Allerton Press, Inc.