The contribution of ammonia-oxidizing archaea and bacteria to gross nitrification under different substrate availability
Tobias Rütting, Philipp Schleusner, Linda Hink, James I. Prosser
Abstract
The first step of autotrophic nitrification is performed by ammonia-oxidizing archaea (AOA) and bacteria (AOB). Recent studies show that their relative contributions are determined by the substrate sources and availability, yet evidence provided by quantification of their respective gross activities in soil is lacking. Here, we conducted a microcosm study with agricultural soil with high (50 μg N g−1) and low (5 μg N g−1) ammonium application, and quantified gross nitrification rates using 15N-tracers. AOA and AOB activities were distinguished using the bacterial inhibitor 1-octyne and acetylene, which inhibits both AOA and AOB. Under low ammonium supply, AOA and AOB contributed equally to gross ammonia oxidation, but AOB outcompeted AOA under higher ammonium supply. These results provide the first direct evidence that substrate availability affects the relative contribution of AOA and AOB to gross nitrification.