ObjectiveThe relationship between nitrogen mineralization in forest soil litter layer (O layer) and surface mineral soil (A layer) under different altitudes of different forest types and soil physical and chemical properties was studied in order to better understand the mineralization potential law of nitrogen under different forest types in the northern forest soil, and to understand the nitrogen cycle of forest soil more fully.

MethodThe method of laboratory aerobic culture was used to study the litter layer and surface soil layer of Pinus pumila forest, Rhododendron dauricum-Betula platyphylla forest, Rhododendron dauricum-Larix dahurica forest, Ledum palustre-Larix dahurica forest, brown coniferous forest soils and bleached podzolic soils in Huzhong Nature Reserve in Daxing’an Mountains’ cold-temperate forest area of China. The physicochemical properties of ammonium nitrogen, nitrate nitrogen, total nitrogen, organic matters, organic carbon, water content, pH and soil mechanical composition were measured at the time of culture, and the relationship between nitrogen mineralization and incubation time and altitude in the soil under 4 forest types was studied, and the regularity of nitrogen mineralization was discussed by principal component analysis to find potential driving factors.

ResultAmmonification is dominant in the 4 types of forest litter, and nitrification is dominant in the surface mineral soil. The mineralized nitrogen content in the litter layer increases first and then decreases with the prolongation of the culture time. The mineralized nitrogen content in the surface mineral soil decreases first and then increases with the prolongation of the culture time, and there is an obvious late period of mineralization in the early stage of culture. The amount of nitrogen mineralization decreased with the elevation rises. pH and environmental factors (water content) have a direct impact on nitrogen mineralization in surface soil, and organic matters, organic carbon, total nitrogen and soil mechanical composition are the main driving factors in the process of soil nitrogen mineralization.

ConclusionNitrogen mineralization characteristics in litter layer and surface mineral soil of different forest types in cold temperate forest areas lead to different trends of nitrogen mineralization due to the difference of cultivation time. Both levels show that with the increase of altitude, the amount of nitrogen mineralization decreases. Through comparative analysis, the changing trend of nitrogen mineralization potential of forest soil in cold temperate forest region can be deeply understood. The results provide scientific basis for further understanding of nitrogen cycle in forest soil.