Effects Of Simulated Nitrogen Deposition On Soil Nitrogen Mineralization In Quercus Acutissima Forest In Urban And Rural Areas

Soil nitrogen content plays a key role in the growth and development of plants.In recent years,the large-scale development of modern industry and agriculture has led to the rapid increase of atmospheric nitrogen deposition.Its influence on the forest ecosystem has attracted the attention of many scholars,but most of them aimed at the natural forests far away from cities.The development of China is the interweaving of industrialization and urbanization,and the production and living of human beings will inevitably affect the circulation of the ecosystem.However,the effect of nitrogen deposition on soil nitrogen mineralization in urban areas and its mechanism are rarely studied.Therefore,the same species of Quercus Acutissima forest at different distances from Hefei City were taken as the research objects,and the Zipeng Mountain in Hefei City was set as the urban group,and the Wanfo Mountain in Shucheng County,Lu'an was set as the rural group.Three nitrogen treatment groups were established by simulating nitrogen deposition:Control(CK,0 kg N·ha^-1·yr^-1),low nitrogen(LN,50 kg N·ha^-1·yr^-1)and high nitrogen(HN,100 kg N·ha^-1·yr^-1).Exogenous nitrogen was applied every two months and soil samples of the0-10 cm and 10-30 cm soil layers were collected and returned to determine and analyze relevant soil indicators.The results of the study are as follows:(1)The contents of ammonium nitrogen(NH₄⁺-N),nitrate nitrogen(NO₃^--N)and soluble organic nitrogen(DON)in soil decreased with the deepening of soil layer.The soil inorganic nitrogen was mainly NH₄⁺-N,and the seasonal change had a significant effect on it.Nitrogen addition had no significant effect on the contents of NH₄⁺-N,NO₃^--N and DON in the soil of urban areas in spring and summer,but had a promoting effect in autumn and winter.Nitrogen treatment increased the contents of NH₄⁺-N,NO₃^--N and DON in rural soil,but in the 0-10 cm soil layer,the effect of high N treatment was inhibited,and the effect of high N treatment in the 10-30 cm soil layer was higher than that of low N treatment.(2)Nitrogen treatment had significant effect on soil microbial biomass carbon(MBC)content.In urban areas,the addition of nitrogen in the 0-10 cm soil layer had inhibition effect,while the low nitrogen in the 10-30 cm soil layer promoted and the high nitrogen in the 10-30 cm soil layer inhibited.In the 0-10 cm soil layer of rural areas,low nitrogen treatment promoted the growth and high nitrogen treatment inhibited the growth.Low N addition promoted the content of MBN in rural soil,but the effect of N addition on soil microbial biomass nitrogen(MBN)and MBC/MBN was not significant overall.(3)Nitrogen treatment had significant effects on ammoniation rate,nitrification rate and mineralization rate,but the forms were different in different regions,soil layers and months.The ammoniation rate and mineralization rate in urban areas were promoted by nitrogen addition.In rural areas,the addition of low nitrogen in the 10-30 cm soil layer promoted the ammonification rate,nitrification rate and mineralization rate.(4)Nitrogen treatment had no significant effects on soil p H,C/N and DOC.The soil electrical conductivity(EC)value was significantly affected.Low nitrogen addition had a promoting effect,while high nitrogen treatment had a lower promoting effect than low nitrogen addition or even an inhibitory effect.The ammoniation rate,nitrification rate and mineralization rate were significantly related to microbial biomass,p H,EC,Doc,water content and so on.