Pakistan Journal of Biological Sciences1028-88801812-5735Asian Network for Scientific Information10.3923/pjbs.2003.1631.1640AzamF. FarooqS. 122003618Symbiotic nitrogen fixation by legumes is the major natural process of adding nitrogen into the biosphere amounting to about 35 million tons annually. The process of nitrogen addition to the ecosystems and its further fate is such as to pose minimum threat to environmental cleanliness relative to N used as chemical fertilizers. Therefore, it has been of great interest not only to understand the basics of nitrogen fixation process but also to quantify the amount of N added to a system under different conditions. This is important in order to quickly screen the available germplasm for its potential of biological N2 fixation and to devise strategies for further improving the process under different ecological conditions. 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Yazaki,198615N among plant parts and in 15N/14N fractionation during N-2 fixation in the legume-rhizobia symbiotic system.]]>27791799