Collaborative Research: Does competition for nitrogen between autotrophs and heterotrophs control carbon fluxes in the western coastal Arctic?

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Bronk 0909839Virginia Institute of Marine ScienceUnds are provided to investigate the microbial controls on the productivity of a coastal Arctic ecosystem by focusing on the competition between autotrophs and heterotrophs for nitrogen (N). In the winter and summer waters near Barrow, Alaska, supplemented with complementary international research opportunities, the PIs propose to measure in situ concentrations of key microbial and biogeochemical constituents, relevant uptake activities, and expression of key N cycling genes to address two hypotheses:H1: The balance of autotrophy and heterotrophy in the Arctic is regulated both temporally and spatially by nitrate (NO3ˉ) and light.? Phytoplankton out-compete heterotrophic bacteria for NO3ˉ during the well-lit spring and summer conditions.? Heterotrophic bacterial uptake of NO3ˉ will be greater during the dark winter and under sea ice than in open water or well-lit summer conditions when bacteria are replete with phytoplankton-derived DON.? NO3 -, combined with terrestrial DOC derived from riverine and groundwater flow, may provide the means for bacterial growth and respiration during the dark winter.H2: Microbial community structure will vary according to the seasonal light cycle and the sources of available N. The observed lag in bacterial response to phytoplankton growth is due to a community shift.? Bacterial community composition will vary significantly between winter and summer.? The composition and dynamics of bacterial communities will correspond to concentrations and sources of N.? The expression of key N-cycling genes, N-uptake and regeneration, and DON uptake kinetics will vary with season and community composition.