Cell specific primary production of autotrophic and mixotrophic phytoplankton in acidified lakes of the Bohemian Forest

Grain density autoradiography was used to study primary production of individual species or genera in two acidified lakes in the Bohemian Forest (Central Europe). Chrysophytes and dinoflagellates were present in both lakes during the studied season, green algae and filamentous cyanobacteria were observed especially in Plešné Lake. In Certovo Lake, the primary production of Dinobryon pediforme was on average 0.56 µg l-1 h-1 C (38 % of total primary production - PT) at the surface layer and 0.20 µg l-1 h-1 C (25 % of PT) at the metalimnetic depth. Peridinium umbonatum accounted for 27 % of PT(0.65 µg l-1 h-1 C) and 31 % of PT (0.22 µg l-1 h-1 C) at each depth, respectively. In Plešné Lake, Monoraphidium cf. dybowskii comprised an almost identical portion of PT at both layers (63 % of PT). Peridinium accounted for 5-29 % and 1-14 % of PT at each depth. Significant seasonal differences in photosynthetic activity coefficients (PAC; the cell-carbon specific rate of C assimilation) were found as well as differences in PAC between individual species, between the same species in different lakes and in different layers of each lake. The PAC of the mixotrophic bacterivorous Dinobryon was equal or even higher than that of autotrophic species, indicating that it uses ingested bacteria as a source of phosphorus rather than of carbon.