Heavy nitrogen application increases soil nitrification through ammonia-oxidizing bacteria rather than archaea in acidic tea (Camellia sinensis L.) plantation soil.

Nitrogen (N) fertilizer is widely used in agricultural ecosystems and influences N transformation processes in the soil such as nitrification. However, whether nitrification is primarily dominated by ammonia-oxidizing bacteria (AOB) or archaea (AOA) under heavy N application is still under debate. In the present work, the effect of long-term (12 years) N fertilization on soil nitrification and the key influencing factors were investigated in acidic tea plantation soil that received four different rates of N application (0, 119, 285, and 569 kg N ha yr). Nitrification potential was measured and partitioned using chemical inhibitors. The abundance of functional genes involved in ammonia oxidation was quantified using quantitative polymerase chain reaction (qPCR). Ammonia-oxidizing communities were identified by shotgun metagenome sequencing. Potential nitrification rate in tea plantation soil was mainly dominated by autotrophic nitrification (PNR) (71-79%). PNR and heterotrophic nitrification (PNR) were both significantly increased by heavy N (569 kg ha) application. Moreover, PNR was mainly due to the contribution of AOB (52-66%) in N-treated soils, and N569 significantly increased the AOB contribution without affecting the AOA contribution. N569 increased the functional gene abundance of AOB and TAO100 (a non-halophilic γ-AOB) but decreased that of AOA. The dominant AOB (Nitrosomonas, Nitrosospira, and Nitrosococcus), AOA (Nitrososphaera and Nitrosopumilus) and commamox (Nitrospira) groups were profoundly altered by long-term N application rates. Partial least squares regression showed that total nitrification (PNR), PNR, and PNR were primarily explained by the functional gene abundance of nitrifiers whereas PNR and PNR were closely associated with soil and pruned litter properties. Moreover, structural equation modeling (SEM) revealed that long-term N application significantly and indirectly affected nitrification potential by directly influencing soil properties, pruned litter properties, and functional gene abundance. Understanding the relative contribution of AOA and AOB to nitrification may help to better regulate N fertilizer use in agricultural ecosystems.