第一节 The nitrogen cycle Various bacteria return the reduced forms of nitrogen back to the environment by oxidizing them. The oxidation of nh4 to NO3 is performed by nitrifying bacteria. Nitrate nitrogen also returns to the atmosphere as n2 as result of the metabolic activity of denitrifying bacteria.第一节 The nitrogen cycle Various bacteria return the reduced forms of nitrogen back to the environment by oxidizing them. The oxidation of NH4 + to NO3 - is performed by nitrifying bacteria. Nitrate nitrogen also returns to the atmosphere as N2 as result of the metabolic activity of denitrifying bacteria