Abstract:Tempo-spatial variations in soil net nitrogen (N) mineralization and nitrification in four typical temperate forests in northeast China were investigated with a PVC tube sequential coring and in\|situ incubation method. The forests were hardwood broadleaf (HB), Quercus mongolica (QM), Pinus koraiensis (PK) and Larix gmelinii (LG) forests. The N mineralization showed significant tempo\|spatial variability in the four forests. The highest net N mineralization rates occurred in June for the QM and PK, and in July for the HB and LG. The rates of N mineralization and nitrification at the upper\|layer soil were greater than those at the lower\|layer. Nitrification was the dominant process in the forests, and the proportion of NO-3\|N to the total inorganic N was 79.9%-91.1%, 50.7%-80.5%, 54.1%-92.0% and 63.7%-86.5% for the HB, QM, PK and LG, respectively. The N mineralization capacity differed significantly among the four forests. The mean rates of N mineralization for the HB, QM, PK and LG were (0.58±0.01) mg·kg-1·d-1, (0.47±0.19) mg·kg-1·d-1, (0.39±0.11) mg·kg-1·d-1 and (0.23±0.06) mg·kg-1·d-1, respectively. The N mineralization was positively correlated to the soil temperature at 5 cm depth for the four forests. This relationship was significantly influenced by the soil moisture at 0-10 cm depth. The N mineralization was also significantly positively correlated to the microbial biomass N.