The Dynamic Soil Nitrogen Mineralization Rate Of Dahurian Larch (Larix Gmelinii) Forest During Different Restoration Periods After Fire Disturbance In Greater Xing’an Mountains

Fire disturbance has been one of the important disturbance factors of Greater Xing’an Mountains forest ecosystem in China.Nitrogen is the most important nutrient elements in the boreal forest ecosystem,study the effects of fire disturbance on soil nitrogen mineralization is of great significance for in-depth study of boreal forest ecosystem recovery mechanism after the fire disturbance.In this study,we investigated the growing season dynamic of Dahurian Larch（Larix gmelinii）forest soil nitrogen mineralization of three different restoration stages after high burning severity fire disturbance（3 year,9 year,28 year）in Greater Xing’an Mountains.We used the in-situ cultivation method to study one growing season soil nitrogen mineralization rate and analysis the impact factors of soil nitrogen mineralization.The results of this study indicated that:Growing season soil ammonium nitrogen（NH₄⁺-N）and nitrate nitrogen（NO₃^--N）of three different restoration stages shown similar variation pattern,which was increased at the beginning of growing season and then decreased at the end of growing season,and the upper layer（0-10m）soil NH₄⁺-N and NO₃^--N of three restoration stages were all higher than that in the lower layer soil（10-20cm）.The soil NH₄⁺-N content after 3 years fire disturbance was higher than that in unburnt control plots,while the soil NH₄⁺-N content was lower than unburnt control plots after 9 and 28 years fire disturbance.The average NH₄⁺-N in three different restoration stages were 82.99mg·kg^-1,93.27mg·kg^-1,108.38mg·kg^-1,respectively.The NH₄⁺-N shown increased trend at different restoration stages after fire disturbance.The soil NO₃^--N after 3 and 9 years fire disturbance was higher than that of unburnt control plots,and the NO₃^--N after fire disturbance 28 years was lower than that of unburnt control forest.NO₃^--N in three different restoration stages were 4.66mg·kg^-1,10.07mg·kg^-1,3.59mg·kg^-1,respectively.The soil net nitrogen mineralization（NMR）rate of growing season after fire disturbance was achieved the largest value in May(3.55 mg·kg^-1),while the smallest was occurred in August(-1.96 mg·kg^-1).The average NMR in three different restoration stages soils were 4.66mg·kg^-1,10.07mg·kg^-1,3.59mg·kg^-1,respectively.The soil NMR rate of growing season shown the trend that firstly increased and then decreased at different restoration stages.The pH and K⁺value were significantly correlated with nitrogen mineralization,which indicated that pH and K⁺are the dominant factors for the variability of net nitrogen mineralization rate in Larix gmelinii forest after fire disturbance.This study will provide the data basis for revealing the variability of forest ecosystem soil nitrogen pool after fire disturbance and the forest ecosystem restoration after fire disturbance.