Overview of recent researches on nitrifying microorganisms in soil

Abstract

Nitrogen cycle, a most important elemental cycle in earth ecosystem, is carried out by three major microbial processes including nitrogen fixation, nitrification and denitrification. Nitrification is particularly important in agricultural soil ecosystems because it is involved in nitrogen loss, groundwater pollution by nitrogen leaching, and greenhouse gas nitrous oxide emission. Recent genomic, metagenomic and physiological analysis of nitrifying microorganisms gives new insights into their ecology and functions in soils. In the last decade, there have been a number of important findings regarding nitrification. The discovery of nitrifying archaea and complete nitrifying bacteria has overturned the conventional theory that nitrification is driven by ammonia-oxidizing and nitrite-oxidizing bacteria. Each of the newly discovered nitrifying microorganisms has unique properties, for example, a different affinity for ammonia. These nitrifying microorganisms have been shown to actually play important roles in nitrification in agricultural soils. Soil conditions and agricultural practices such as fertilization and tillage have been shown to influence the contribution of each nitrifying microorganism to the activity of nitrification. In addition, nitrification inhibition technologies have been developed to prevent the loss of nitrogen fertilizer and the of nitrous oxide emission. This review provides an overview of recent researches on the diversity and characteristics of nitrifying microorganisms, soil factors affecting their ecology in soil, their involvement in nitrous oxide emissions, and nitrification control technologies.