All plants require nitrogen in forms they can absorb through their roots, and that accessible nitrogen is provided by certain soil bacteria. while many plants rely on the activity of free-living soil bacteria for ammonium ions (nh4+) and nitrate ions (no3−), some plants form extremely close symbiotic relationships with nitrogen-fixing bacteria. for example, rhizobium bacteria (one type of nitrogen-fixing bacteria) take up residence inside the root cells of legume plants, which include peas, soybeans, and clover. in this activity, you will indicate how the legumes and the rhizobium bacteria are affected by this symbiosis.