Ammonia oxidizing archaea do not respond to ammonium or urea supply in an alkaline soil

Vasileios A.Tzanakakis, Antonios Apostolakis, Nikolaos P.Nikolaidis, Nikolaos V.Paranychianakis

Region of Crete, Directorate of Agricultural Economy, Iraklion 71201, Greece.

Abstract

Strains of ammonia oxidizing archaea (AOA) can utilize urea under limited conditions of ammonia in terrestrial environments. In this work, we investigate whether this mechanism operates more widely, including soils with non-limiting conditions of ammonia. To test this hypothesis, pots filled with a soil of basic pH (8.3) were supplied with two rates of N (25 and 50 μg N/g dry soil) in the form of urea and ammonium applied at seven consecutive doses every 2 days. The findings of the study revealed a strong increase in the abundance of ammonia oxidizing bacteria (AOB) at both application rates, independently of N source. By contrast, AOA did not respond to N additions. These findings indicate that urea availability does not offer an advantage on the growth and activity of AOA over the AOB under non-limiting conditions of N. However, a slight increase in AOA abundance following substrate utilization provided support for a link between AOA growth and mineralization of soil organic matter.

Keywords: Nitrification, Mineralization, Urea, Nitrogen cycling, Alkaline soil, AOA, AOB.