Fig. 5: Conceptual summary of acidification effects on ammonia oxidation across different aquatic ecosystems.
From: Ammonia oxidizers offset acidification stress via adaptive substrate affinity in aquatic ecosystems

The diagram illustrates the shift from ammonia-oxidizing bacteria (AOB) dominance in eutrophic zones to ammonia-oxidizing archaea (AOA) dominance in oligotrophic zones. Blue bars represent ammonia oxidation rates under substrate-limited conditions, and red bars represent rates under substrate-saturated conditions. Dotted-line arrows indicate the effect of reduced substrate availability, whereas solid-line arrows indicate the effect of increased substrate affinity. Arrow thickness reflects the relative strength of each effect. Under future scenarios of acidification, in substrate limitation conditions, ammonia oxidation rates are expected to decrease in freshwater and the open ocean but increase in the outer estuary.