Evidence of heterotrophic prokaryotic activity limitation by nitrogen in the Western Arctic Ocean during summer
Global warming in the Arctic Ocean may result in changes to the stock and dynamics of nutrients that drive the activity of heterotrophic prokaryotes, a key component of the microbial food web. We performed 14 enrichment experiments during summer in the Beaufort and Chukchi Seas (Western Arctic Ocean), with C (acetate and/or glucose), N (nitrate and/or ammonium) and P (phosphate) amendments. In 8 out of 11 experiments performed with surface waters, prokaryotic heterotrophic production was limited by N, either alone (5 experiments) or in co-limitation with C (3 experiments). This contrasted with the experiments performed using waters from the chlorophyll maxima, where N was never limiting. Diversity analyses (DNA- and RNA-based fingerprinting) suggest that limitation was not restricted to specific operational taxonomic units but common to the different groups. This is the first report of N limitation of prokaryotic heterotrophic production in Arctic surface waters. This control by N may gain importance in future scenarios of higher productivity in the area.
KeywordsHeterotrophic prokaryotes Production Abundance Community structure Nutrient limitation Arctic Ocean
This work was supported by the French National Research Agency, under the grant no. ANR-BLAN08-1_310980 to the MALINA project, the LEFE-CYBER and CNES TOSCA programs, and the European Space Agency. W.H.J was supported by a University of West Florida faculty scholarly and creative activity award. Research in the Chukchi Sea was possible thanks to the logistic offered by the NASA Icescape program. We thank R. Benner Y. Shen and C. Fichot for DOC data, S. Bélanger and K.R. Arrigo for chl a data, Y. Gratton and J. Swift for CTD data, J.E. Tremblay, P. Raimbault and J. Swift for nutrients data and D. Marie for in situ bacteria counts in 2009. We thank the editor and three anonymous reviewers for constructive comments in a previous version of this MS.
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