Nitrite oxidizing bacteria, Nitrobacter and Nitrospira, are differently influenced by season, fertilizer, and tillage in long-term maize culture

Abstract

Nitrite (NO2−) oxidation is the second step in nitrification, following ammonia (NH3) oxidation, and catalyzed by nitrite oxidizing bacteria (NOB). Their activity is critical in preventing toxic accumulation of NO2−. The two major NOB genera in soil are Nitrobacter and Nitrospira. This study investigated how N fertilization and tillage management influenced these two NOB communities in long-term (>40 years) maize (Zea mays L.) cropping. To evaluate NOB community changes we used PCR and denaturing gradient gel electrophoresis (DGGE) to analyze Nitrobacter and Nitrospira NO2− oxidoreductase genes (nxr). Season, fertilizer rate, and tillage all influenced Nitrobacter and Nitrospira communities, but differentially for the two genera. Nitrobacter was more diverse in summer, whereas Nitrospira was more diverse in winter. Nitrobacter was more diverse in N-fertilized samples, whereas Nitrospira diversity decreased with increasing fertilizer rate in winter but not summer. Nitrobacter diversity was not significantly influenced by tillage, whereas no-tillage samples had more diverse Nitrospira, compared to plow tillage samples. In addition to providing evidence for better understanding the relationship between soil management and NOB communities, this study also helped to suggest linkages between ammonia oxidizing bacteria and Nitrobacter and between ammonia oxidizing archaea and Nitrospira that may facilitate future studies concerning ammonia-oxidizing nitrifiers and NOB.