Diel periodicity in ammonium uptake and regeneration in the oceanic subarctic pacific implications for interactions in microbial food webs

Wheeler, P.A.; Kirchman, D.L.; Landry, M.R.; Kokkinakis, S.A.

Limnology and Oceanography 34(6): 1025-1033


ISSN/ISBN: 0024-3590
DOI: 10.2307/2837192
Accession: 007204963

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Diel periodicity in NH4+ uptake and regeneration in the nutrient-rich environment of the oceanic subarctic Pacific was examined. Surface water was incubated in large shipboard microcosms that allowed repeated sampling of the planktonic community for NH4+ cycling rates, bacterial production rates, and population densities of the dominant autotrophs and heterotrophs. Changes in NH4+ concentrations and isotopic enrichments indicated that regeneration took place exclusively at night. Nitrogen uptake rates and bacterial production were maximal during the day. Abundance of >2-.mu.m autotrophic flagellates reached a maximum at the end of day or beginning of night, whereas abundance of zooflagellates in the >2-.mu.m and 1-10-.mu.m size classes showed a twofold variation with maximal abundances occurring at the beginning of day. These contrasting diel patterns suggest short-term, cyclic disequilibrium in production and grazing within the microbial food web. Hence, analysis of relationships among the various components of microbial populations in this type of environment will reqquire sampling on much shorter time scales than has been attempted in past studies.