Effects Of Simulated Warming On Soil Nitrogen Mineralization And N₂O Emission In Pinus Tabulaeformis Plantation In Daqingshan Mountains

Daqing Mountain is located at the intersection of moderate temperate steppe and warm temperate steppe in the Mongolian Plateau.It is the best preserved secondary forest area in the middle section of Yinshan Mountain.It is very representative of climate,soil,geology and geomorphology,flora and fauna,showing ecological diversity and sensitivity to climate change.Climate warming affects the nitrogen cycle and greenhouse gas emissions of forest ecosystems by affecting plant photosynthesis fixation,respiration,and litter decomposition.Taking Pinus tabulaeformis plantation in Daqingshan region of Inner Mongolia as the research object,this paper compared the effects of temperature increase on the key processes of soil nitrogen cycle in the plantation through artificial simulated temperature increase.In this study,two treatments(CK,Control)and(OTC,Warming)were set.Soil mineralization rate was measured by buried tube method,N₂O emission was measured by static chamber gas chromatography,and environmental factors such as soil and atmospheric temperature and humidity were measured simultaneously.In this study,we combined the methods of variance analysis,correlation analysis and factor analysis to explore the main factors affecting forest soil nitrogen mineralization and N₂O emission under the background of warming.Research shows that:(1)Under simulated warming treatment,the atmospheric temperature increased by0.72?,the annual atmospheric humidity increased by 0.39%,and the soil temperature of each layer increased by 1.09?,1.25?,1.14?and 0.59?,respectively.The soil temperature at 10 cm was the highest,and the soil temperature at 40 cm was the lowest.(2)The surface soil water content was significantly reduced by-3.63%,while the deep soil water content(40 cm)had no obvious response to the warming,but increased by 1.20%under the warming treatment.The soil water content of the artificial pine forest in Daqing Mountain of Inner Mongolia from July to September was higher than that in other months of the same year.Excess precipitation offset the effect of temperature increase on the soil water content of the artificial pine forest.(3)The changes of soil nitrogen in different soil layers were consistent under warming treatment.The soil N mineralization rate was significantly promoted by increasing temperature,and the soil N mineralization rate decreased with increasing temperature.In both 0-10 cm and 10-20 cm soils,the ammonium,nitrification and nitrogen mineralization rates reached the maximum values in August,which was the most favorable time for soil nitrogen mineralization.Soil ammonium rate,nitrification rate and nitrogen mineralization rate ranged from-0.06 to 1.12(mg/kg/d),from-0.13 to 0.06(mg/kg/d),and from-0.06 to 0.17(mg/kg/d)in 0-10 cm soil.(4)The temperature increase reduces the seasonal variation value of N₂O emission flux,which ranges from 1.97 to 9.73(ug.m^-2.h^-1)in OTC treatment and from 3.39 to12.70(ug.m^-2.h^-1)in CK treatment.(5)Soil ammoniation rate,nitrification rate,nitrogen mineralization rate and N₂O emission flux were all positively correlated with soil water content.Soil N₂O emission flux is mainly affected by soil temperature and soil p H.The higher the soil temperature is,the greater the effect on soil N₂O emission flux is.The higher the soil p H,the greater the soil N₂O emission flux.