Abundance and community structure of ammonia-oxidizing bacteria and archaea in purple soil under long-term fertilization

Ammonia-oxidizing microorganisms, which drive the first and rate-limiting step in the process of nitrification, play an important role in soil N-cycling processes. However, little is known about the ammonia-oxidizing bacteria (AOB) and archaea (AOA) in purple soils, which are characterized as lithologic soils without distinct pedogenic horizons and are mainly distributed in the Sichuan basin of Southwestern China. Here, the abundance and community structure of AOB and AOA in a 21-year fertilization experiment were investigated by real-time PCR and terminal restriction fragment-length polymorphism (T-RFLP), respectively. In the present study, nine different fertilization treatments were examined: NPK fertilization plus pig manure (NPK + M), NPK fertilization (NPK), without fertilization (CK), pig manure fertilization (M), P with NH4Cl and KCl plus pig manure (Cl + M), PK fertilization (PK), NK fertilization (NK), NP fertilization (NP), and N fertilization (N). Our results indicate that N-fertilized treatments have higher AOB abundances than the control (CK) and treatments without N amendment. The lowest AOA abundance and AOA/AOB ratios were observed in the treatment (Cl + M) with long-term application of NH4Cl plus KCl. The AOB community structure under combined addition of N and P differed from that under other treatments. The Cl + M treatment had a distinct AOA community structure and higher diversity compared with other treatments. Moreover, higher potential nitrification rates (PNR) were found in the combined N and P addition treatment groups than that in the other treatment groups, and the lowest PNR and pH (<6) were detected in the Cl + M treatment. These results highlight that not only nitrogen but also phosphorus may be a crucial factor affecting soil ammonia-oxidizing activity and triggering changes of AOB community composition. Moreover, soil pH might have an essential role in controlling the AOA community structure and ammonia-oxidizing activity in purple soil. (C) 2013 Elsevier Masson SAS. All rights reserved.