Abstract: In this experiment，two heterotrophic nitrifying bacteria isolated from lawn soil were identified by comparing 16S rDNA sequence to homologous species published on the GenBank. The nitrification function of these two bacteria were detected by measuring intermediate products，denitrification process and N2O emission characteristics under inorganic nitrogen sources （NH4+-N and NO3--N）. The results showed that the two heterotrophic nitrifying bacteria were identified as Pseudomonas sp.，16S rDNA fragment length were 1 448 and 1 460 bp and named as Pseudomonas sp. BJ and Pseudomonas sp. DJ，respectively. GenBank accession number were MF001078 and MF001079 for Pseudomonas sp. BJ and Pseudomonas sp. DJ. The two strains have a strong oxidation ability with inorganic nitrogen，ammonium removal efficiencies were 96.61% and 97.06%，respectively. The maximum nitrification rate were 21.97 and 18.90 mg ? L-1 ? h-1. Denitrification ability of two bacteria were not efficient，the maximum denitrification rate were 0.99 and 1.00 mg ? L-1 ? h-1，respectively. Metabolic pathways of the two strains can be simplified to a large extent as NH4+ → NH2OH → NO2- → NO3-. NO3--N was the main intermediate products of strain DJ，and its content was much higher than that of strain BJ（P < 0.05）. The content of N2O produced by strain BJ was significantly higher than that of strain DJ（P < 0.05）.

Key words: lawn soil, heterotrophic nitrifying bacteria, nitrification characteristic, N2O emission