Nitrite　as　an　important　substrate　for　Anammox　can　be　provided　by　partial　denitrification　(PD).　In　this　study,　endogenous　partial　denitrification　(EdPD)　and　exogenous　partial　denitrification　(ExPD)　sludge　were　domesticated　and　their　nitrite　transformation　rate　reached　74.4%　and　83.4%,　respectively.　The　impact　of　four　carbon/nitrogen　(C/N)　ratios　(1.5,　3.0,　5.0　and　6.0)　on　nitrous　oxide　(N2O)　emission　and　denitrification　functional　genes　expression　in　both　PD　systems　were　investigated.　Results　showed　that　elevated　C/N　ratios　enhanced　most　denitrification　genes　expression,　but　in　EdPD,　high　nitrite　levels　suppressed　nosZ　genes　expression　(from　9.4%　to　1.4%),　leading　to　increased　N2O　emission　(0　to　3.4%).　EdPD　also　exhibited　lower　electron　transfer　system　activity,　resulting　in　slower　nitrogen　oxide　conversion　efficiency　and　more　stable　nitrite　accumulation　compared　to　ExPD.　These　findings　offer　insights　for　optimizing　PD　systems　under　varying　water　quality　conditions.　©　2024