Ecology of Denitrifying Prokaryotes in Agricultural Soil

Denitrification is a microbial respiratory process during which soluble nitrogen oxides are used as an alternative electron acceptor when oxygen is limiting. It results in considerable loss of nitrogen, which is the most limiting nutrient for crop production in agriculture. Denitrification is also of environmental concern, since it is the main biological process responsible for emissions of nitrous oxide, one of the six greenhouse gases considered by the Kyoto protocol. In addition to natural variations, agroecosystems are characterized by the use of numerous practices, such as fertilization and pesticide application, which can influence denitrification rates. This has been widely documented in the literature, illustrating the complexity of the underlying mechanisms regulating this process. In the last decade, however, application of molecular biology approaches has given the opportunity to look behind denitrification rates and to describe genes, transcripts, and enzymes responsible for the process. In order to reduce denitrification in arable soil, it is important to understand how different factors influence denitrification and how the denitrifier community structure is related to in situ activity. This chapter focuses on the impact of natural events as well as agricultural practices on denitrifying microorganisms.