Nitrogen cycling is one of the important elements geobiochemical circulations and plays an irreplaceable role in element balance. Nitrification is an essential process in the global N cycle in which ammonia (NH₃) is biologically oxidized to nitrate (NO₃-) by ammonia oxidizers. As the first and rate-limiting step of nitrification, ammonia-oxidizing microorganisms were studied by many researchers. They reported that soil pH, temperature, moisture, organic matter and fertilization have made important effects on the composition and activity of these microorganisms in different terrestrial ecosystems. However, little is known about the impact of long-term land use types on composition of their communities in sloped land and the relationship between NO₃-N loss with these microorganisms.

Since 2009, the researchers in Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) have paid attention to the relationship between nitrification with ammonia oxidizers in sloped land. They collected the soil samples from natural forest (NF), cropland (CL), and tea plantation (TP) plots in a long-term sloped land use experiment at the Taoyuan Agro-ecosystem Research Station. They found that land use types induced significant changes in soil potential nitrification rate and community composition, diversity, and abundance of both ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). Both AOB and AOA community compositions were similar between upper and lower slope positions (UP and LP) in NF and TP. While in CL, it was significantly higher diversity and abundance of both AOB and AOA in the LP than the UP. Among the land use types, the NO₃-N and AOA runoff loss was greatest in CL. NO₃-N runoff loss was significantly correlated with the loss of AOA in the runoff water. Furthermore, they found that the NO₃-N runoff loss had a significant relationship with the abundance of AOA but not of AOB at both slope positions. These findings suggested that AOA were more important than AOB in nitrification and NO₃-N runoff loss in acidic soils across sloped land use types.

The main findings of this study have published on Biol Fertil Soils, and the detail can be reached at http://link.springer.com/content/pdf/10.1007%2Fs00374-012-0767-1.pdf

This research was financially supported by the National Basic Research Program of China (973 Program, 2012CB417106), the key project for the Twelfth Five-Year Plan of China (2012BAD14b03), and the National Natural Science Foundation of China (41271280, 40801098).