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AME prepress abstract   -  DOI: https://doi.org/10.3354/ame01993

Nitrogen-carbon association influences the response of the microplankton food web to enrichment

Junwen Guo*, Sonia Brugel, Agneta Andersson, Mehdi Cherif

*Corresponding author:

ABSTRACT: In aquatic ecosystems, there are 2 major forms of nitrogen available at the base of the planktonic food web: dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN). In DON, nitrogen is associated with organic carbon, which may promote both heterotrophs and autotrophs. In environments where DIN-nitrate is the prevailing nitrogen form and dissociated dissolved organic carbon (DOC) is available, heterotrophs may also be promoted, but they may compete with the autotrophs for DIN. The influence of associated or dissociated carbon-nitrogen nutrient sources on the interaction between organisms and the food web function is poorly known and has not been studied before. To approach this question, we performed a microcosm experiment with a coastal microbial food web, where nitrogen and carbon nutrient sources were provided either associated in one molecular compound DON or dissociated in 2 separate molecular compounds DIN and DOC. The results showed that association or dissociation of carbon and nitrogen input had marked effects on all trophic levels, most probably through its effect on bacteria–phytoplankton interaction, which switched between increased coupling and increased competition. The biomass of all components of the food web benefited from the association of C and N in a single DON molecule. Our study indicated that the degree of association between C and N is an important factor affecting the productivity and efficiency of the microbial food web. Therefore, the carbon and nitrogen association should be considered when studying aquatic systems.