PRODUCTION OF DISSOLVED ORGANIC NITROGEN DURING UPTAKE OF NITRATE BY SYNEDRA-PLANCTONICA - IMPLICATIONS FOR ESTIMATES OF NEW PRODUCTION IN THE OCEANS

Nitrate uptake was measured in batch cultures of the unicellular alga Synedra planctonica. During the light period, extensive excretion of dissolved organic nitrogen occurred, which represented up to 63% of nitrate uptake between 2 and 4 h into the light period. During the following dark period, most of this excreted nitrogen was taken up by dividing cells. New production can be underestimated by 50% if such a phenomenon occurs during uptake measurements restricted to the light period.