Primary production and heterotrophy of a pennate and a centric salt marsh diatom

Radionuclide labeled sodium bicarbonate and glucose were used to measure the rates of primary production and glucose uptake by Nitzschia obtusa var. undulata and Cymbella pusilla. The presence of glucose in the medium enhanced primary production in both diatom species. Uptake of glucose in C. pusilla was photoinhibited. A maximum of 9.3 nmol C mg dry wt^-1 h^-1 of glucose was taken up in the light without the presence of NaHCO₃ in the medium and with NaHCO₃ present the value was 18 nmol C mg dry wt^-1 h^-1. The ratio of inorganic carbon fixed to the total carbon budget (autotrophy and heterotrophy) was 0.51 for N. obtusa var. undulata and 0.62 for C. pusilla.