Nitrogen Cycle Proteins and waste products Microbial decompositionAmino acids Amino acids (-NH2) Microbial ammonificaionAmmonia (NHa) Nitrosomonas Ammonium ion(NH4) →Nitrite ion(NO2） Nitrobacter Nitrite ion(NO2) Nitrate ion (NO3) Pseudmonas Nitrate ion (NO3 N2 Nitrogen-fixation N2 Ammonia(NH3) Nitrogen Cycle N2 Nitrogen - fixation Ammonia (NH3 ) Nitrate ion (NO3 - ) Pseudmonas N2 Nitrite ion (NO2 - ) Nitrobacter Nitrate ion (NO3 - ) Ammonium ion (NH4 + ) Nitrosomonas Nitrite ion (NO2 - ) Amino acids (–NH2 ) Microbial ammonification Ammonia (NH3 ) Proteins and waste products Microbial decomposition Amino acids