4. Discussion
Nitrogen addition showed significant effects on several biotic
and abiotic soil properties in this study. With increase of nitrogen
addition rate, Soil pH and potential nitrification rate declined,
while AOB abundance increased gradually. Increase of AOB abundance
with N addition were also found in some other studies [7–
14], and the positive correlation between AOB abundance and
ammonia concentration in this study further indicated the importance
of ammonia for AOB growth. Some other researches reported
that ammonia oxidization were driven mainly by bacteria in some
croplands and croplands with high concentration of N addition,