Vertical niche differentiation of comammox Nitrospira in hydro-fluctuation zone soil of the Three Gorges Reservoir Region

Abstract

Abstract CMX NB can accomplish ammonia oxidation independently, and its niche differentiation holds a promise for its ecological and survival function. In this work, the vertical niche differentiation of comammox (CMX) Nitrospira bacteria (NB) was investigated in the soils of 6 hydro-fluctuation (HF) zones (both natural and artificial) in the Three Gorges Reservoir (TGR) Region. The results demonstrated that the level of clade A amoA was obviously reduced with the increasing soil depth in the natural HF zone and one of the artificial HF zones. However, in the other two artificial HF zones, the abundance of this gene was not dramatically reduced along the depth. The level of clade B amoA was not markedly decreased with the increasing soil depth in most HF zones, and remained stable in three HF zones. Total nitrogen had the most significant effect on the abundance of CMX NB. Clade A.1, A.2.1, A.2.2, A.3, and B of CMX NB co-occurred simultaneously in all HF zones. The number of operational taxonomic units (OTUs) of clade A in the two types of HF zones was first elevated and then reduced with the increasing depth, whereas the number of OTUs of clade B was continuously increased with depth in the artificial HF zone. pH and total carbon (TC), as environmental factors, affected the community structure of CMX NB. This study confirmed the vertical differentiation of the abundance and diversity of CMX NB in the HF zone of the TGR area, and the artificial restoration of the HF zone affected the niche differentiation of CMX NB to a certain degree.