The Effects Of Simulated Nitrogen Deposition On Nitrogen Dynamics And Emissions Of Greenhouse Gases In Artificial Young Forest Soil

With population growth and economic development, human activities havesignificantly altered the global nitrogen cycle, resulting in increasing Nr（reactive nitrogen） in the atmosphere, which can lead to increasing nitrogendeposition in terrestrial ecosystems and aquatic ecosystems. Global warming isone of the most serious climate change problems. As the source and tank ofgreenhouse gases, forest ecosystem plays an important role in climate change.With the background of increasing nitrogen deposition and global warming, afield experiment using NH₄NO₃as nitrogen source in Schima superb artificialyoung forest was conducted in Zengcheng Guangzhou to study the response ofthe soil nitrogen dynamics and soil greenhouse gases （CH₄、CO₂、N₂O）emissions to3levels of simulated nitrogen deposition (N0,0g N m^-2yr^-1; N5,5gN m^-2yr^-1; N10,10g N m^-2yr^-1). The analysis results of topsoil （0-20cm）,0-60cmsoil and the fluxes of CH₄、CO₂、N₂O shows that:（1） Soil carbon, including organic carbon and inorganic carbon, does notchange significantly from November2012to April2013. Organic carbon is themajor form of soil carbon, it shows a similar trend with total carbon and totalnitrogen: decreases with the depth.（2）Adding nitrogen does not change the content of soil total nitrogen,which showed no significant changes from November2012to April2013.（3） Using NH₄NO₃as nitrogen source, pH showed a downward trend inthree levels with the increase of soil depth, which means a risk of soilacidification. pH of NO, N5, N10in the depth of0-60cm are7.01±0.06⁵.93±0.04，697±0.10⁵.84±0.20，6.81±0.10⁵.72±0.29, respectively. （4） Nitrate of N5and N10is higher than N0in the depth of0-60cm. In thedepth of0-20cm, nitrate of N0, N5,N10are0.94±0.07⁴.45±0.61mg kg^-1，0.97±0.04⁹.03±1.38mg kg^-1,1.17±0.08⁵.42±2.86mg kg^-1, respectively.（5）In the depth of0-20cm, ammonium is at a low level and significantlylower than the control group （N0）, while in the deeper layers, ammonium showsa higher content, which poses a threat to groundwater. In the depth of0-60cm,concentrations of ammonium of N0, N5, N10are0.19±0.21⁰.81±0.06mgkg^-1,0.14±0.13⁰.89±0.10mg kg^-1,0.23±0.09¹.08±0.20mg kg^-1.（6） Microbial biomass （Lipid-P） differs significantly at different nitrogendeposition level, and there are peak values in the depth of30-40cm at bothlevels of N5and N10.（7） Nitrogen deposition affects the emission of CO₂more in spring（P=0.077） than in winter （P=0.292）. The emission of CO₂exhibits positiverelationship with nitrogen deposition level. Flux in the afternoon differs a lot（P=0.015） from the morning in one day.6days after fertilization, CO₂emissionis higher at N5and N10lever than N0.(8The emission of N₂O shows no significant at3nitrogen deposition levelexcept on2013.4.27（6days after fertilization）, which is significant higher thanin2013.4.21. Short-term nitrogen deposition increase may lead to the growth ofN₂O emission of artificial young forest soil.