RESOURCE COMPETITION THEORY EXPLAINS TRADEOFF BETWEEN DISSIMILATORY NITRATE REDUCTION TO AMMONIUM AND DENITRIFICATION

Organic matter (OM) loading is a ubiquitous anthropogenic disturbance in aquatic ecosystems which alters nutrient cycling dynamics. Not only does OM loading introduce mineralizable nutrients, but it may also create anoxic microsites on sinking particulates which support anaerobic processes in otherwise oxic waters. Furthermore, OM loading may promote an electron donor rich environment, thus altering microbial metabolic competition dynamics. The combination of anoxia and electron donor availability alters the biogeochemical landscape and, as one example, dictates the degree to which bioavailable nitrogen (N) is retained in an ecosystem (via dissimilatory nitrate reduction to ammonium, DNRA), rather than converted to nitrous oxide or dinitrogen gas (via denitrification). To improve our predictive abilities of these critically important transformations, we developed a microbial population model that mechanistically resolves the competition of DNRA and denitrification for nitrate (or nitrite) under varying OM loading intensities. The redox chemistry underlying each metabolism informs the model parameters, providing a theoretically grounded quantitative framework. In the model, when the ratio of OM to nitrate supply is sufficiently high such that nitrate becomes limiting, DNRA can competitively exclude denitrification. As the redox-constrained parameters may be more broadly applicable than species or location-specific parameters, our framework can aid in improving our understanding of N cycling in environments where microbial community dynamics are largely unknown.

Primary Presenter: Jemma Fadum, Carnegie Science, Stanford (jfadum@carnegiescience.edu)

Authors:

Jemma Fadum, Carnegie Science, Stanford  (jfadum@carnegiescience.edu)

Emily Zakem, Carnegie Science, Stanford  (ezakem@carnegiescience.edu)