To understand the relative importance of plant community composition and plant-induced soil properties on N transformations, the soil N mineralization, ammonification and nitrification characteristics of natural secondary forests (Quercus mongolica-Juglans mandshurica forest: QJF, and Quercus mongolica-Populus davidiana forest: QPF) and the adjacent larch plantations (Larix kaempferi forest: LF1 and LF2) were studied during the growing season. All of the forest types showed seasonal dynamics of N mineralization rates. The total cumulative N mineralization was significantly higher in QPF (73.51 kg hm⁻²) than in LF1 (65.64 kg hm⁻²) and LF2 (67.51 kg hm⁻²) (p < 0.05). The total cumulative nitrification from May to November was significantly higher in QJF (65.16 kg hm⁻²) and QPF (64.87 kg hm⁻²) than in LF1 (52.62 kg hm⁻²) and FL2 (54.17 kg hm⁻²) (p < 0.05). Based on the variation partitioning, independent soil properties were the primary determinants of the N transformations (13.5%). Independent climate conditions explained 5.6% of the variations, while plant variations explained 3.2% of the variations in N transformations. We concluded that different forest types with various plant community compositions have different influences on the litterfall quantity and quality and the nutrient availability, and these differences interact with seasonal climate conditions that in turn drive the differences in N mineralization.