Fertilization has a greater effect than rhizosphere on community structures of comammox Nitrospira in an alkaline agricultural soil

Abstract

The discovery of comammox Nitrospira has expanded our knowledge of classical labor division in nitrification and opened up new avenues to unravel the nitrification process in terrestrial ecosystems. However, the effects of fertilization and rhizosphere on comammox Nitrospira remains largely limited, especially in alkaline agricultural soils. To address this knowledge gap, the community structure of comammox Nitrospira and canonical ammonia oxidizers in the bulk and rhizosphere of an alkaline agricultural soil following 8 years of fertilizer applications was investigated. The fertilization treatments included no fertilization (CON), mineral NPK fertilizer (NPK), manure + straw (MS), NPK + manure (NPKM), NPK + manure and straw (NPKMS), and NPK + manure and straw by deep ploughing (NPKMSD). Five phylogenetic clusters of comammox Nitrospira were detected in the soil including clades A.1, A.2.1, A.2.2, A.3 and B, with A.2.1 and B as the dominant clades. Fertilization had a greater effect than rhizosphere on the community structure of comammox Nitrospira, while both fertilization and rhizosphere had no significant effect on the community structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Compared with CON and NPK, the relative abundance of comammox Nitrospira clade A, especially clade A.2.1, increased while clade B decreased following manure applications. Soil nitrate played a critical role in driving the variation of comammox Nitrospira community structure. These findings showed novel evidence of niche specialization of comammox Nitrospira and canonical ammonia oxidizers in agricultural soils.