Ammonia-oxidizing microorganisms: key players in the promotion of plant growth

Nitrogen (N) is the most important mineral nutrient required by plants.Although some plants can directly utilize N, ammonium (NH 4 + ) and nitrate (NO 3 -) are the only forms of N that are usable to most plants.Ammoniaoxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) are the key drivers that are responsible for the conversion of N into usable forms.Due to the importance of ammonia oxidizers (AOs), factors affecting their abundance and activity have been a major research focus over the years.This review focuses on the diversity of AOs, the factors that affect their abundance and activity in different soil types and the mechanism of nitrifica-tion.An improved understanding of the combinatorial effects of highly active AOs and methods for limiting nitrate loss from soils may enhance the management of nitrate in soils and improve plant yields.