The nitrogen cycle

Abstract

This chapter focuses on the nitrogen (N) cycle, a complex network of mainly microbial transformations in which various nitrogen compounds are interconverted. Both microorganisms and plants absorb N from and excrete N into the environment. First, N assimilation is addressed (22.1), after which N transformations by microorganisms are described (22.2). In paragraph 22.3 both plant and microbial N cycling are discussed at the ecosystem level, followed by paragraph 22.4, where the use of N by humans and the consequences for the N cycle are reviewed. Finally, in 22.5 the conclusions and outlook are presented.