Nitrous oxide production by nitrogen-fixing, fast-growing Rhizobia.

Rhizobium trifolii, R. leguminosarum, andR. "hedysarum", grownex planta under anoxic conditions in a chemically defined medium, evolve N2O from NO3 (-), NO2 (-), and (NH4)2NO3. The amount of nitrous oxide formed after 96 hours is about 0.2μM×mg(-1) cells d.w. Large availability of organic matter enhances the production of N2O from nitrate by free-livingR. trifolii in peat/sand mixtures. Denitrification of the above species andR. meliloti was detected also in planta. Nitrous oxide production increases almost linearly from 10-45μM×mg(-1) nodules d.w. when nitrogen-fixing plants are exposed to increasing concentrations of nitrate (1-12μM).