DIAZOTROPH: A FRIEND OR FOE OF PLANTS
Biological Nitrogen (N) fixation is the major natural process through which atmospheric dinitrogen (N2) is converted into forms that can be used by plants and animals, contributing 100-290 TgN per year to the biosphere Cleveland et al., 1999. Although the majority of Nitrogen (N) fixation in terrestrial ecosystems is carried out by symbiotic bacteria in association with plants, free-living diazotrophs in soils have been shown to be important contributors to the Nirogen (N) budgets of a number of ecosystems (shi-fang and Daniel 2008). Progress in understanding the ecological significance of free-living diazotrophs has been limited, however, by the fact that many of these organisms are recalcitrant to laboratory cultivation. The nifH gene, which encodes a subunit of the nitrogenase enzyme, Provides a useful market that can be used to study the distribution and diversity of diazotrophs without the need for cultivation (Buckley et al., 2007).