Contribution of Bacteria to Initial Input and Cycling of Nitrogen in Soils

Abstract

Nitrogen was discovered by the Scottish chemist and physician Daniel Rutherford in 1772 by removing oxygen and carbon dioxide from air. At the same time, the French chemist, Antoine Laurent Lavoisier, isolated what we would call nitrogen and named it azote, meaning without life since it did not support life or combustion. However, nitrogen is the fourth most common element in many biomolecules, which are essential for life, being outrankedonly by carbon, hydrogen andoxygen. Thus, nitrogen is found in amino acids that form proteins and in the nucleoside phosphates of nucleic acids. The cycle of nitrogen in soil has been studied more extensively than any other nutrient cycle. Nevertheless, despite decades of investigations by microbiologists of the different steps of the nitrogen cycle, many of these are still poorly understood or quantified. One striking aspect of theN cycle is the coexistence in nature of different oxidation states of the nitrogen atom ranging from reduced compounds, e. g., −3 as in ammonia to fully oxidized state, e. g., +5 as in nitrate. The conversion between the different forms of nitrogen is mediated by processes performed by soil microorganisms. Together these processes form the global nitrogen cycle and living organisms are essential formaintaining the balance between nitrogen’s reduced and oxidized forms. The aim of this chapter is to provide an introductory-level survey of the main microbial processes that participate in the N cycle, to present recent data on the diversity and the distribution of the bacteria involved in these different processes, and to give an estimation of N fluxes within the N cycle.