production of cotton, rice, wheat, peanuts, rape, corn, sorghum, potatoes, tobacco, sugarcane and various vegetables. Importance In terms of generating nitrogen available to all organisms, the symbiotic associations greatly exceed the free-living species with the exception of cyanobacteria. Diazotroph plays an important roles in nitrogen cycle of the earth. In the terrestrial ecosystem, the diazotroph fix the (N2) from the atmosphere and provide the available nitrogen for the primary producer. Then the nitrogen is transferred to higher trophical levels and human beings. The formation and storage of nitrogen will all influenced by the transformation process. Also the available nitrogen fixed by the diazotroph is environmentally sustainable, which can reduce the use of fertilizer, which can be an important topic in agricultural research. In marine ecosystem, prokaryotic phytoplankton (such as cyanobacteria) is the main nitrogen fixer, then the nitrogen consumed by higher trophical levels. The fixed N released from these organisms is a component of ecosystem N inputs. And also the fixed N is important for the coupled C cycle. A greater oceanic inventory of fixed N may increase the primary production and export of organic C to the deep ocean. References External links Marine Nitrogen Fixation - The Basics (USC Capone Lab) Azotobacter Rhizobia Frankia & Actinorhizal Plants Nitrogen cycle Environmental microbiology