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

Abstract

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 15 N‐labeled glycine and glutamic acid ranged from 0.001 to 0.002 µ g‐atom N/hr‐ µ g‐atom particulate N, compared to 0.03 to 0.05 for nitrate and ammonia. Uptake experiments using both 15 N‐ and 1 4 C‐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 15 N‐labeled nitrate released about 10% of the 15 N back into the seawater as dissolved organic nitrogen within 48 hr. This value is probably conservative by virtue of the experimental procedure.