Ammonia-uptake kinetics and domain-level contributions of bacteria and archaea to nitrification in temperate forest soils

Ammonia-oxidizing bacteria and archaea (AOA and AOB) perform the rate-limiting step of nitrification, a biogeochemical process that controls the availability of inorganic nitrogen in terrestrial and aquatic ecosystems. We sought to investigate field values of AOA and AOB ammonia-uptake kinetics along with domain-level contributions to ammonia oxidation in temperate forest soils. To accomplish this goal, we constructed an ecosystem model that simulates ammonia oxidation in temperate forest soils based only on inorganic nitrogen pools and AOA and AOB population dynamics observed during in situ incubations. The model used Bayesian Markov chain Monte Carlo procedure to choose the most likely combination of in situ ammonia-uptake parameters for AOA and AOB, including Km,AOA, Km,AOB, Vmax,AOA, and Vmax,AOB. Domain-level contributions to ammonia oxidation were extracted from the best-fit solution and the model-selected values indicate that AOB was responsible for 70.0% of the simulated ammonia oxidation across sites, while AOA was responsible for the remaining 30.0%. We believe that the approach we demonstrate here can be applied to microbially-mediated biogeochemical fluxes in other elemental cycles as well.