Potential correlated environmental factors leading to the niche segregation of ammonia-oxidizing archaea and ammonia-oxidizing bac-teria: A review

Ammonia oxidation is an important step of the nitrogen cycle and was considered to be conducted only by ammonia-oxidizing bacteria (AOB) for a long time. The discovery of ammonia-oxidizing archaea (AOA) caused consideration of the relative contributions of these two functional groups in different niches and factors resulting in their niche segregation. Previous studies showed that some environmental factors may correlate to the abundance and distribution of AOA and AOB, including ammonia/ammonium concentration, pH, organic matters, oxygen concentration, temperature, salinity, sulfide concentration, phosphate concentration, soil moisture and so on. Despite extensive studies conducted on ecology of AOA and AOB to find key environmental factors dominating niche segregation between AOA and AOB, few studies were conducted to explore the interrelationship among environmental factors. In this review, five main environmental factors which may be related to each other were selectively reviewed independently, including ammonia concentration, pH, temperature, oxygen concentration and organic matters. Furthermore, potential interrelationship among environmental factors was proposed.