Research On Forest Soil NO Flux At Different Elevation And Slope Posotion Of Huoditang Area In The Qinling Moutains

Nitrogen oxides play a crucial role in atmospheric chemistry.Although NO is a relatively short-lived species in the troposphere and therefore has mostly local and regional effects on atmospheric photochemistry,regional and global inventories are necessary to put the strength of the soil source of NO into perspective with other natural and anthropogenic sources.NO fluxes are known to vary considerably with both soil temperature and soil moisture.However,the relationships are not simple.There is no clear conclusion between them.It is therefore important to study these relationships over a range of climates at long time-scales to cover different seasons for each locality.In this paper we report the results of continuous measurements of NO fluxes at different elevations（1560²160m）and slope positions of Huoditang Area in the Qinling Mountains from October 2014 to October 2015 using the static chamber technique and NOx analyzer（ML 9841 B Nitrogen Oxides Analyzer）.The main results are as follows:（1）The majority of NO fluxes occurred during growing season from May 2015 to September 2015,but NO emitted at a low level.During non-growing season from October 2014 to April 2015,NO fluxes in most of the sample plots decreased first and then increased and NO uptake was found during the detecting period.Annual NO fluxes were between 0.02 and 0.19 kg·ha^-1·yr^-1.Annual NO fluxes decreased with increasing altitude except for the Pinus armandii forest.The maximum annual NO fluxes were on the middle slope(0.11 kg·ha^-1·yr^-1),and then the upper slope(0.09 kg·ha^-1·yr^-1)and the lower slope(0.06 kg·ha^-1·yr^-1).（2）Across elevations,NO fluxes were significantly correlated with soil temperature（P<0.05）.NO fluxes in the Pinus armandii forest（1963 m）was negatively correlated with WFPS（P<0.05）.NO fluxes in the Pinus tabulaeformis forest（1585m）was negatively correlated with NH4+ concentrations（P<0.05）,while the rest were not related.Soil NO fluxes on the upper slope were significantly correlated with soil temperature and WFPS（P<0.05）.Soil NO fluxes on the middle slope were very significantly correlated with soil temperature（P<0.01）and negatively correlated with NH4+ concentrations（P<0.05）.Soil NO fluxes on the lower slope were positively correlated with soil temperature and NO3-concentrations（P<0.05）.（3）Soil temperature was the main factor affecting soil NO fluxes.Soil WFPS in all sampling pots was always below 60% except for the Pinus tabulaeformis forest（1963 m）,suggesting that nitrification was the important source of NO in this region.But denitrification was accompanied with the influence of precipitation and soil physicochemical properties.