Redox-constrained microbial ecology dictates nitrogen loss versus retention

Area of Science:

• Microbial ecology
• Biogeochemical cycling
• Ecosystem modeling

Background:

• Microorganisms are key drivers of biogeochemical cycles.
• Eutrophication in aquatic systems with deep anoxic waters increases surface productivity, impacting anaerobic microbial communities.
• Increased sinking organic carbon can shift microbial function from nitrogen loss to retention, creating a positive feedback loop that amplifies eutrophication.

Purpose of the Study:

• To develop a quantitative, first-principles model of the transition from nitrogen loss to retention in anaerobic microbial communities.
• To link microbial ecological dynamics to the energetics of microbial metabolisms.
• To understand the impact of increasing organic carbon supply on nitrogen cycling.

Main Methods:

• Developed and analyzed an ecosystem model incorporating redox chemistry.
• Constrained traits of key anaerobic nitrogen-cycling microbial functional types: denitrification, dissimilatory nitrate reduction to ammonium, and anaerobic ammonium oxidation (anammox).
• Linked ecological dynamics to microbial metabolism energetics.

Main Results:

• The model successfully captures the transition from nitrogen loss to retention with increasing organic carbon supply.
• Identified characteristics of microbial community composition at the "net zero N loss" point.
• Provided testable hypotheses for sequencing data and other observations.

Conclusions:

• The model offers a mechanistic understanding of nitrogen cycling shifts due to eutrophication.
• Results provide a broadly applicable framework for predicting biogeochemical impacts of perturbations like eutrophication and deoxygenation.
• Tying microbial ecology to environmental chemical potential enhances predictive capabilities for aquatic ecosystems.