Abundance and community composition of ammonia oxidizers in rhizosphere sediment of two submerged macrophytes.

Ammonium oxidation is both the first and a rate-limiting step in the nitrification process that can be catalysed by ammonia-oxidizing archaea (AOA) or ammonia-oxidizing bacteria (AOB). In this study, the abundance and community composition of AOA and AOB in the rhizosphere sediments of two submerged macrophytes (Ceratophyllum demersumandPotamogeton malainus) were investigated. Physicochemical parameters, including pH, total nitrogen, total phosphorus, ammonia nitrogen, nitrate and organic matter, were measured. The number of copies of both the archaeal and bacterialamoAgene was quantified by real-time PCR and clone libraries were constructed for both AOA and AOB. The abundance of archaealamoAgene ranged from 3.83 × 106to 4.23 × 106copies per gram of dry sediment and no significant difference was found among the three treatment groups (one control group and two submerged macrophyte groups). The abundance of bacterialamoAgene ranged from 2.68 × 106to 8.05 × 107copies per gram of dry sediment. Bulk sediment maintained significantly higher copy numbers of bacterialamoAgene than those ofC. demersumrhizosphere sediment. The diversity of archaealamoAgene was higher in the rhizosphere sediment ofC. demersum; however, the diversity of bacterialamoAgene was relatively lower in rhizosphere sediment of both macrophytes. [ABSTRACT FROM PUBLISHER]