Uptake and regeneration of free amino acids in marine waters of Southeast Alaska1

The nutritive importance of dissolved organic nitrogen to phytoplankton populations was assessed in Auke Bay, Alaska. Nitrate, ammonia, total dissolved organic nitrogen, and dissolved free amino acids were monitored and related to phytoplankton growth. Uptake rates of 15N‐labeled glycine and glutamic acid ranged from 0.001 to 0.002 µg‐atom N/hr‐µg‐atom particulate N, compared to 0.03 to 0.05 for nitrate and ammonia. Uptake experiments using both 15N‐ and 14C‐labeled glycine and glutamic acid showed that the nitrogen of glycine is preferentially incorporated, the carbon being respired; the reverse is true for glutamic acid, the nitrogen presumably being released as ammonia. Phytoplankton supplied with 15N‐labeled nitrate released about 10% of the 15N back into the seawater as dissolved organic nitrogen within 48 hr. This value is probably conservative by virtue of the experimental procedure.