Deposition Of Atmosphere Nitrogen Indicated By The Nitrogen Isotopic Compositions (δ¹⁵N) Of The Camphor Tree Leafage In Nanchang

With the industry economic and other human activities development, atmospheric nitrogen deposition which has caused people's attention caused a series of ecological damage at city area. In order to discuss the reliability of vascular plants used as biological indicator to monitor atmospheric nitrogen pollution,the spatial distribution of atmospheric nitrogen deposition of Nanchang city and trace atmospheric nitrogen source, this paper packed 155 camphor tree leaves and 22 soil samples in 10 sampling sites of five functional zones in Nanchang city,and measured their nitrogen contents,nitrogen isotope values, specific leaf area and leaf area.By combining plant bionidicator method with isotopic technique, this paper was mainly contrast theirδ15N in camphor tree leaves of different functional zones for indicating environmental conditions and atmospheric N deposition. By investigating factors affecting leaves isotopic signatures, the mechanisms of leaves isotopic responses to environmental factors and N deposition were disccussed. By using elemental contents and isotopes in camphor tree leaves, and combining with other factors,N deposition at Nanchang area was systematically studied.This paper has deepened the application of leaves isotopes for monitoring environment and N deposition, and it has provided geochemical references for the prevention and control of N pollutants at city area. Some significant innovations have been obtained.To contrast N% andδ15N in camphor tree leaves of different functional zones:The tissue nitrogen content of residential area was higher than other functional zones and besides motorway,the tissue N% of traffic zones was less than that of industrial zones.It appeared that where atmospheric nitrogen concentration is high, tissue nitogen content of leaves was also high, indicating vascular plants can be used as bio-indicator to monitor atmospheric nitrogen pollution.The older leaves had moreδ15N than the younger leaves of coal-based power plant (-2.59%o-3.57%o), highway (-4.42%o-3.04%o) and residential area (-0.79-2.52%o). However, Ammonia Plant(-9.85±0.62‰)had the most negativeδ15N, reflecting that vascular plants can be used as bio-indicator to monitor atmospheric nitrogen pollution source. Tissue nitrogen isotope and nitrogen content of leaves showed no correlation in Nanchang city,which also reflected the complexity of nitrogen sources in Nanchang city.To contrast N% andδ15N in camphor tree leaves of points in different distances from nitrogen point source:In Ammonia Plant and motorway area,The tissue nitrogen content in the nearer point to emission source was more than the further points,indicating that the nearer to the emission source,the more serious nitrogen deposition.In Ammonia Plant,the nearer to emission source,the more negativeδ15N in the leaves, and more negativeδ15N in leaves in the tree tops than that in the tree bottoms.It reflected that the negativeδ15N of ammonia were from Ammonia Plant. However, in the motorway area, the nearer to motorway, the more positiveδ15N in the leaves, and the more positveδ15N in leaves in the tree tops than the bottoms,indicating the positiveδ15N of nitrogen-containing compound from vehicles.Some influencing factors of using camphor tree leaves to monitor nitrogen deposition:some influencing factors such as the leaf area,the soil environment and the season were studied to get more information about using camphor tree leaves to monitor nitrogen deposition.It was found that there were larger specific leaf area(LSA) of leaves in industrial areas than that in residential area and the largest area(S) of leaves in Meiling,infecting that leaves in pollution area had larger LSA and smaller S.Tissue nitrogen and soil nitrogen showed a linear correlation y=0.27+5.60 x (R2=0.621,p<0.01)in Nanchang city. However,onlyδ15N of leaves and soil had linear correlation in no-pollution area, insteading of pollution area.It could be due to influence of the pollution atmosphere coming from the pollution area on the leaves.This study analysed leaves of Meiling packed in spring and fall. The analysis showed that there was no significantly difference in tissuse nitrogen content between two seasons,andδ15N of leaves in spring(-0.34±0.23%o) was significantly lower (p<0.05) than that in fall (0.31±0.23%o),possibly owing to the different sources in two seasons,which also needs more evidence.