Dissolved organic nitrogen release and bacterial activity in the upper layers of the Atlantic Ocean.

Microbial Ecology
Marta M VarelaJoaquín Valencia

Abstract

The variability of the percentage of extracellular dissolved organic nitrogen (DON) release (PER), along with the relationship between DON release and bacterioplankton activity, was examined during five oceanographic cruises, carried out in the upwelling region of the NW Iberian Peninsula, the SW Bay of Biscay, and a latitudinal transect in the Atlantic Ocean (50 degrees N-35 degrees S). Rates of nitrogen uptake, DON release, and bacterial production were measured at 66 stations and sampled between August 1998 and October 2000. The percentage of DON release relative to the gross uptake of ammonium (PERNH4+) ranged from 3 to 46%, whereas that relative to total nitrogen (NH4+ + NO3- + urea) gross uptake (PERtotal) varied between 21 and 82%. The highest values for both PERNH4+ and PER(total) were found in oligotrophic oceanic waters (< 0.25 mg chlorophyll a m(-3)). In oceanic environments, a positive relationship was found between nitrogen uptake and DON release rates, with a log-log linear regression slope significantly lower than 1, suggesting an inverse relationship between PER and gross nitrogen uptake rates. In contrast, in areas with higher productivity levels (> 6 mg chlorophyll a m(-3)), such as the continental shelf off t...Continue Reading

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