Effects Of Simulated Canopy Nitrogen Deposition On Soil Fauna In Southern And Northern Subtropics

With the global nitrogen deposition situation is more and more serious,a lot of nitrogen compounds are still continuously discharged into the atmosphere.These nitrogen compounds can be reduced to forest ecosystem by dry deposition and wet deposition,which threatens the structure and function of forest ecosystem.In the past,the experiments were carried out the traditional way of understory nitrogen deposition.The physiological and ecological processes of canopy response to the nitrogen deposition were neglected.Canopy responses to the nitrogen deposition are include canopy interception,changes of soil moisture,canopy leaf nitrogen,litter and soil microbes and so on.90% of atmospheric material has to through the canopy reach the ground.Therefore,the method of canopy nitrogen deposition is considered to be the closest to the reality of atmospheric nitrogen deposition to forest ecosystem.The field-control experiment platform of simulated canopy nitrogen deposition is in Guangdong Province,South subtropical monsoon region Shimentai National Reserve and Henan Province,North subtropical monsoon region Jigongshan National Reserve.The nitrogen deposition is divided into 5 kinds: 0 kgNha^-1yr^-1 control group(CK,0 kg N ha^-1 yr^-1),canopy nitrogen 25(CN25,25 kg N ha^-1 yr^-1),canopy nitrogen 50(CN50,50 kg N ha^-1 yr^-1),understory nitrogen 25(UN25,25 kg N ha^-1 yr^-1)and understory nitrogen 50(UN50,50 kg N ha^-1 yr^-1).The soil samples were taken in November 2014 and in November 2015 for studying the difference between canopy nitrogen deposit and traditional understory nitrogen deposit on soil animals and the difference of soil fauna's response to canopy nitrogen: deposition in different climatic zones.The results showed that:?1?In Shimentai,the individual number,group number and DG index of soil animal decreased with the increasing canopy nitrogen application time.The higher concentration(50 kg N ha^-1 yr^-1)of canopy nitrogen deposition,the individual number,group number and DG index decreased significantly?p<0.05?.The individual number \group number of soil animals increased with the increasing understory nitrogen application time.Compared with the traditional understory nitrogen application,the canopy nitrogen deposition has significantly negative effect on soil fauna.?2?In Jigongshan,no matter canopy nitrogen deposition or understory nitrogen deposition,the individual number and group number increased with the nitrogen application time.The lower nitrogen concentration(25 kg N ha^-1 yr^-1)treatment group CN25 and UN25's individual number and group number in November 2015 were significantly higher than those in November 2014's?p<0.05?.However,no matter canopy nitrogen deposition or understory nitrogen deposition,the DG index decreased with nitrogen application time.The DG index of treatment group UN50 in November 2015 was significantly lower than the November 2014's?p<0.05?.?3?The individual number and group number of Jigongshan increased with the canopy nitrogen application time.The lower nitrogen concentration(25 kg N ha^-1 yr^-1)treatment group CN25's individual number and group number in November 2015 were significantly higher than those in November 2014's?p<0.05?.The soil fauna in different climatic zones have different response to canopy nitrogen deposition.