title: Biological and ecological aspects of nitrogen fixation by free-living micro-organisms.
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D003081:Cold Climate; D004463:Ecology; D056890:Eukaryota / Q000378:metabolism*; D005658:Fungi / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism; D008982:Molybdenum / Q000378:metabolism; D009586:Nitrogen Fixation; D010100:Oxygen / Q000378:metabolism; D012988:Soil Microbiology; D014871:Water Microbiology; D015003:Yeasts / Q000378:metabolism
chemical_list: D008982:Molybdenum; D007501:Iron; D010100:Oxygen