Key Processes and Prokaryotes in the Nitrogen Cycle Processes Example organisms 硝化 Nitrification (NH,+>NO2) NH4t→NO2 Nitrosomonas NO2→NO3 Nitrobacter 反硝化 Denitrification (NO3->N2) Bacillus,Paracoccus, Pseudomonas 固氨 N,Fixation (N2 8H->NH3 H) Free-living Aerobic Azotobacter Cyanobacteria Anaerobic Clostridium,purple and green bacteria Symbiotic Rhizobium Bradyrhizobium Frankia 氨化 Ammonification (organic-N->NH") Many organisms can do this硝化 反硝化 固氮 氨化