Their functions are different because their raw materials are different. Nitrifying bacteria add free nitrogen or nitrates to the soil by the process of nitrification.Ammonifying bacteria convert ammonia into nitrates which is converted into free soil nitrogen by nitrifying bacteria.
@Ashutosh Choudhary...yes it is about redox potential. when the number of plants are low in wetland bedand redox potential is more than -250 mV in top surface zone: does ammonifying bacteria have better hand over nitrifying bacteria near the root zones of plants present?