WANG Yan-li 1,2, XIAO Hua-yun1,*, XIAO Hongwei1,2, ZHU Renguo1,2

 （1. State Key Laboratory of Environment Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China；
2. Graduate University of Chinese Academy of Sciences, Beijing 100049, China）

Abstract: This article deals with the responses of ecological system to atmospheric nitrogen deposition. Leaves of Osmanthus Fragrans were collected since Mar. 2009 till Mar. 2010, in an urban area at Guiyang. We measured nitrogen content and isotopic composition of leaves with different canopy thickness, sampling positions were specifically identified. Results turned out that the temporal variation of foliar N% and d15N showed higher levels in Spring/ Winter, lower levels in Summer/Autumn. That variation trend is consistent with the monitoring data of rainwater in Guiyang. In the case of upper and lower canopies, a decrease in N% of leaves was associated with an increase in canopy thickness, and the upper canopy has the most negative d15N, while the lower one has more positive isotopic values. These results can be interpreted as that isotopic fractionation happened during uptake of atmospheric N by leaves. In canopy retention processes there is 15N discrimination, causing the isotope ratios to deviate from the atmospheric nitrogen deposition, and giving rise to the d15N of lower canopy. This summary coupled with the results of other experiments supported the conclusion that vascular leaves can be used as a robust marker of atmospheric N sources, which can boost the prevention of eco-environmental deterioration.

Key words: Osmanthus Fragrans; foliar N% and d15N; atmospheric nitrogen deposition; canopy thickness

EARTH AND ENVIRONMENT Vol. 40, No.2, Tot No.288, 2012, Page 148-153