1. Introduction
Nitrogen accumulation in Inner Mongolia of China is increasing
in many soils which mainly results from nitrogen fertilization
accompanied with conversion of large area of grasslands to croplands.
Nitrification is a central process for nitrogen cycle and plays
important roles in soil nutrient and nitrate pollution which is
mainly driven by microorganisms, yet the effects of nitrogen accumulation
on nitrification and related microorganisms have not
been well studied in Inner Mongolia.
Ammonia-oxidization microorganisms catalyzed the key step of
nitrification which were mainly composed of ammonia-oxidizing
bacteria (AOB) and ammonia-oxidizing archaea (AOA). Ammonia
oxidation is considered to be finished mainly by AOB in most studies
for a long time, but some recent studies showed a probable
important role of AOA in ammonia oxidization [1–3]. Study on
both AOB and AOA were necessary to understand the ammonia
oxidization process. Due to the diverse phylogeny and physiological
characteristics of AOB and AOA, it is important to learn the
environmental factors related to the composition and activity of
AOB and AOA to elucidate their functions in various ecosystems.
Based on the long-term fertilization experiment in Inner Mongolia,
the composition of AOB and AOA were investigated with