Short-term Effects Of Simulated Nitrogen Deposition On Soil Nitrogen Transformation In Urban And Rural Environmental Gradient Forests

Human industrial and agricultural activities affect the global ecosystem nitrogen cycle,which is manifested by the rapid increase of nitrogen deposition in terrestrial ecosystems,affecting ecosystem nutrient cycling.Compared with other terrestrial ecosystems,urban soil nitrogen cycle research is still in its infancy.With the acceleration of urbanization,more and more natural land and agricultural land have become urban land,and urban expansion has increasingly affected the soil nitrogen cycle.Appearance,therefore,the study of simulated N sedimentation is of great significance for the mechanism of nitrogen transformation in urban forest soils.So far,there are few reports on the response of nitrogen conversion in urban forests to nitrogen deposition and the effects of N mineralization factors,and the mechanism is still unclear.To this end,this study used the Quercus acutissima Carruth.forest widely distributed in Hefei as the research object.According to the urban-rural environmental gradient,select the Zipeng Mountain(urban area)of Hefei City and Wanfo Mountain of Shuan County of Lu,an County.(rural area)for the experimental plot,using the simulated nitrogen deposition method,in addition to the control(0 kg N ha-1·yr-1),two nitrogen treatments were set:low nitrogen(50 kg N ha-1 ·yr-1)and high nitrogen(100 kg N ha-1·yr-1).The dynamic changes of soil nitrogen in the soil of the paralyzed forest were studied under different nitrogen addition gradients.The characteristics of soil nitrogen mineralization under different nitrogen addition levels were analyzed,and the main factors affecting the nitrogen mineralization of urban forest soil by nitrogen deposition were discussed.Reveal the mechanism of nitrogen deposition on soil nitrogen conversion in urban forests.To provide a scientific basis for a correct understanding of urban soil carbon sequestration,biological earth nitrogen cycling,and rational nitrogen application in people's production practices.The research results are as follows:(1)The monthly variation trend of NH4+-N and NO3--N content in different soil layers is basically the same,and the contents of NH4+-N and NO3--N decrease with the increase of soil depth.The inorganic nitrogen is mainly NH4+-N.Different environmental gradients in urban and rural areas showed changes in mineralization rate>nitrification rate>ammoniaization rate.In the 0-10 cm and 10-30 cm soil layers,the nitrification rate in urban areas is greater than the ammoniation rate;the nitrification and ammoniation rates in rural areas are relatively stable,indicating that the nitrogen conversion in urban areas is dominated by nitrification and the risk of nitrogen loss High sex.There are differences in the monthly dynamics of different gradient ammoniation,nitrification and mineralization in urban and rural areas.The performance of urban areas decreased first and then increased,and the lowest value appeared in August-October;the performance in rural areas increased first and then decreased,and the maximum appeared in August-October.(2)Short-term simulated nitrogen deposition has no significant effect on ammoniation,nitrification and mineralization of urban and rural environmental gradients.Different environmental gradient nitrogen additions in urban and rural areas have an effect on nitrogen mineralization,and fluctuate with seasonal changes,but there is no obvious law.Different nitrogen treatments in urban and rural areas have basically increased the amount of nitrification and mineralization in August-October.The interaction of N treatment and N treatment with other factors had no significant effect on soil ammoniation,nitrification and mineralization rate.The gradient ammoniation rate in urban and rural areas is mostly negative,and the nitrification rate is positive.(3)N treatment has no significant effect on MBC and MBN.The effect of simulated nitrogen deposition on MBC and MBN varies depending on factors such as location,month and soil layer.The monthly variation of MBC and MBN in urban areas under nitrogen deposition was consistent,which was the minimum in December;the rural areas showed the minimum in October.The response of MBC content to different nitrogen treatments tends to be consistent between different soil layers,and MBN has the same pattern.(4)There is a close relationship between soil nitrogen mineralization and microbial biomass carbon and nitrogen under simulated nitrogen deposition.It is further demonstrated that the nitrogen mineralization process is obviously affected by the number and activity of microorganisms.Nitrogen deposition did not reach the threshold of nitrogen stimulation effect of forest soil,which showed that it only had some influence on soil physicochemical properties such as soil pH,water content TN,C/N,available phosphorus and microbial biomass,but the effect has not reached a significant level,so the performance Different nitrogen addition gradients had no significant effect on soil nitrogen mineralization and nitrogen mineralization rate.