Soil type determines the abundance and community structure of ammonia-oxidizing bacteria and archaea in flooded paddy soils

Ammonia oxidation plays an important role in global nitrogen cycle. However, little information is available on ammonia oxidizers in paddy soils. This study aimed to understand the controlling factors of ammonia oxidizers in the paddy soils. Three types of paddy soils were collected from southwest [Chongqing City (CQ)], central [Honghu City (HH)], and northeast [Panjin City (PJ)] of China, respectively. The soils were cultured with unplanted and rice-planted pot experiments for 10 weeks. The abundance and composition of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) of the paddy soil samples were investigated by real-time polymerase chain reaction and denaturing gradient gel electrophoresis approaches based on amoA genes. In this study, minor changes in the abundance and community structure of both AOB and AOA were observed among the treatments of unplanted and rhizosphere and bulk of rice-planted soil samples in the same type of paddy soil. The AOB population sizes in CQ were lower than those in HH and PJ, while the AOA in CQ and HH were lower than those in PJ. The amoA gene copy numbers of AOA were more abundant than those of AOB in all treatments of the three paddy soils. The community structure of both AOB and AOA in all paddy soils was different from each other. The population size and community structure of AOB and AOA in the flooded paddy soils were mainly determined by the soil types, irrespective of rice-planted or unplanted.