Bioavailability of Wetland-Derived DON to Freshwater and Marine Bacterioplankton

Access to bioavailable nitrogen often limits primary production in marine and freshwater ecosystems. Around 70% of nitrogen transported by rivers worldwide consists of dissolved organic nitrogen (DON), but its bioavailability has been poorly investigated. To assess the potential bacterial growth on...

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Bibliographic Details
Published in:Limnology and oceanography 1999-09, Vol.44 (6), p.1477-1485
Main Authors: Stepanauskas, Ramunas, Leonardson, Lars, Tranvik, Lars J.
Format: Article
Language:English
Subjects:
Animal, plant and microbial ecology
Autumn
Bacteria
Bioavailability
Biological and medical sciences
Brackish
dissolved organic nitrogen
Fresh water
Freshwater
Fundamental and applied biological sciences. Psychology
Groundwater
Marine
Microbial ecology
Nitrates
Nitrogen
Sea water
Summer
Sweden
Various environments (extraatmospheric space, air, water)
Wetlands
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Summary:Access to bioavailable nitrogen often limits primary production in marine and freshwater ecosystems. Around 70% of nitrogen transported by rivers worldwide consists of dissolved organic nitrogen (DON), but its bioavailability has been poorly investigated. To assess the potential bacterial growth on DON, we developed a bioassay employing natural DON and bacterial inocula in medium manipulated to make N the limiting nutrient. We analyzed the bacterial utilization of the high-molecular-weight fraction of DON isolated by ultrafiltration from three wetlands in South Sweden throughout the year. The bioavailability of low-molecular-weight and bulk DON was also analyzed in one of the wetlands, where inorganic nitrogen concentration was sufficiently low and did not interfere with bioassays. The bioavailability of bulk DON in the latter wetland varied from 2% to 16%, suggesting that DON is an important nitrogen source for the biota of coastal waters. DON may be the dominant input of bioavailable nitrogen during summer, when nitrate concentrations in rivers decrease and DON bioavailability increases. Marine bacterioplankton assimilated a substantially larger fraction of DON than did freshwater bacterioplankton, on average by a factor of 2.4. This finding indicates that the susceptibility of DON to bacterial mineralization increases as it is transported from freshwaters into saline environments.
ISSN:0024-3590
1939-5590
DOI:10.4319/lo.1999.44.6.1477