[Growth and photosynthetic activity of diatom Thalassiosira weissflogii at decreasing salinity].

The relative yield of variable chlorophyll fluorescence (Fv/Fm), rate of photosynthetic carbon fixation (P), growth rate, and production of extracellular photosynthates (Pec) was studied in diatom T. weissflogii in seawater with salinity decreasing from 35 to 15 and 5 per thousand. After incubation at 5 per thousand for 1 day, the diatom abundance (N) decreased as a result of death of a fraction of cells, while viable cells demonstrated decreased Fv/Fm and P, Pec was detectable, and cell division was likely inhibited. After incubation for 2 days, population started to grow, while exponential growth rate and the abundance by day 8 were lower compared to 35 per thousand. After incubation at 15 per thousand for 1 day, P was higher and Fv/Fm was lower compared to 35 per thousand. No cell death was observed and exponential growth rate insignificantly differed from that at 5 per thousand. The value of N by day 8 was lower compared to 35 per thousand but higher compared to 5 per thousand. The dependence of photosynthetic parameters and population dynamics of T. weissflogii on the relative salinity is discussed.

[Effect of the exogenous glucose on photosynthesis of the diatom Thalassiosira weissflogii depending on nitrate supply and light]. / Vliianie ékzogennoi gliukozy na fotosintez diatomovoi vodorosli Thalassiosira weissflogii v zavisimosti ot obespechennosti nitratami i urovnia osveshchennosti.

The rate of photosynthetic carbon fixation (P) in the diatom Thalassiosira weissflogii cultivated in the presence of exogenous glucose in the medium (0-10.56 micrograms C/l) at different levels of illumination (25, 50, and 100 microE/m2 s) was studied as a function of nitrate nitrogen supply. In the diatoms limited in nitrogen and assimilating exogenous glucose, P was found to decrease or increase depending on light intensity, glucose concentration, and the duration of exposure. In the diatoms assimilating both nitrate nitrogen and glucose, compared to those supplied with nitrates alone, P was higher at medium and high light intensities and lower at a low light intensity. The interrelation of the processes of carbon and nitrogen metabolism in mixotrophic algae and the ecological role of glucose consumption by phytoplankton are discussed.