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| 1. |
which bacteria are needed for theIhstalktion of nitrogen? |
| Answer» <p>microorganisms capable of transforming atmospheric nitrogen intofixed nitrogen(inorganiccompoundsusable by plants). More than 90 percent of allnitrogen fixationis effected by these organisms, which thus play an important role in thenitrogen cycleTwo kinds of nitrogen-fixingbacteriaare recognized. The first kind, the free-living (nonsymbiotic) bacteria, includes thecyanobacteria(or blue-green algae)AnabaenaandNostocand genera such asAzotobacter,Beijerinckia, andClostridium. The second kindcomprisesthe mutualistic (symbiotic) bacteria; examples includeRhizobium, associated with leguminous plants (e.g., various members of thepea family);Frankia, associated with certain dicotyledonous species (actinorhizal plants); and certainAzospirillumspecies, associated with cereal grasses.</p> | |