The emergence of nitrification during DOM processing by marine microbial assemblages

Area of Science:

• Marine microbial ecology
• Biogeochemical cycles

Background:

• Dissolved organic matter (DOM) degradation and nitrification are key ocean processes.
• The interplay between DOM, ammonium, and nitrate dynamics is not fully understood.

Purpose of the Study:

• To investigate the mechanisms driving the succession of DOM degradation and nitrification in marine environments.
• To understand the competitive interactions between heterotrophic bacteria and nitrifiers.

Main Methods:

• Two DOM degradation experiments using natural marine microbial communities and microalgal-derived DOM.
• Monitoring of DOM, ammonium, and nitrate concentrations over 150 days.
• Numerical simulations to model microbial community dynamics.

Main Results:

• Observed ammonium consumption and nitrate increase after 150 days of DOM degradation.
• Nitrifying prokaryote abundance increased as labile DOM decreased.
• Simulations showed nitrifier dominance with increasing DOM recalcitrance.

Conclusions:

• Nitrification emergence is linked to carbon limitation and shifts in microbial competition.
• Heterotrophic bacteria initially dominate DOM degradation, but nitrifiers gain advantage as DOM becomes recalcitrant.
• This study clarifies the feedback loops between DOM cycling and nitrification in the ocean.