Photosynthetic characteristics of the benthic diatom species Nitzschia frustulum (Kutzing) Grunow isolated from a soda pan along temperature-, sulfate- and chloride gradients

The Carpathian Basin hosts a number of small, shallow, saline, alkaline ponds. As being endorheic basins, they are highly threatened by the climate change and response of biota to changing climate has been largely unexplored. We investigated the effects of salinity changes on the photosynthetic activity of Nitzschia frustulum, which is one of the main dominant taxa of the saline lakes in the FertA-Hansag Region of the Carpathian Basin. The photosynthetic activity of the species was measured along temperature (5, 10, 15, 20, 25, 30, 35, 40 A degrees C), light (0-8-35-70-110-200-400-800-1200 A mu mol m(-2) s(-1)), SO4 (2-) (0-50-600-1200-2400-3600-4800 mg L-1) and Cl- (0-36-437.5-875-1750-3500-5250 mg L-1) gradients under laboratory conditions in photosynthetron. The conductivity optimal of N. frustulum was around 5600 A mu S cm(-1) with wide salinity tolerance. The species preferred the HCO3 (-)-SO4 (2-)-type waters since its photosynthetic activity (3.62 mg C mg Chl-a (-1) h(-1)) was more than twice higher than in HCO3 (-)-Cl--type media. Its photosynthesis saturated at very low-light intensity, and photoinhibition was not observed during the experiments. The maximal photosynthesis was measured at 28-29 A degrees C. However, above 30 A degrees C, the decline of photosynthesis of N. frustulum can be forecasted.