pH and ammonium concentration are dominant predictors of the abundance and community composition of comammox bacteria in long-term fertilized Mollisol

Abstract

Abstract The newly-discovered complete ammonia-oxidizing bacteria (comammox) doubts our inherent understanding of nitrification. Herein, we study communities of comammox, ammonia-oxidizing bacteria (AOB) and archaea (AOA) in Mollisol after a 30-year fertilization history with four treatments: chemical nitrogen (N) and potassium (K) fertilizers (NK); chemical N, phosphorus (P), and K fertilizers (NPK); chemical NPK fertilizers plus organic manure (NPKM); and a control without fertilizers (CK). Compared with CK, chemical fertilizer treatments (NK and NPK) significantly reduced AOA amoA gene abundance and increased AOB and comammox amoA gene abundances. The highest values of AOA and AOB amoA gene abundances were found in the NPKM treatment and the highest value of comammox amoA gene abundance was observed in the NK treatment. The application of combined NPK and organic manure (NPKM) significantly increased AOA, AOB, and comammox amoA gene abundances compared to CK. Long-term chemical fertilization decreased the diversity of comammox community; whereas, the application of combined NPK with organic manure (NPKM) restored it to levels comparable to CK. Long-term fertilization management altered the community structure of comammox based on principal coordinate analysis (PCoA). Soil pH and NH4+-N concentration were the key factors affecting soil abundance and community structure of comammox. This study demonstrates the different responses of comammox community and canonical ammonia oxidizers to long-term fertilization practices in Mollisol.