通过对贵阳市法国梧桐叶片为期1 a的监测(2009-03~2010-04),分析其叶片氮含量及氮同位素组成随季节变化的规律,并与同期湿沉降监测结果进行对比,探讨维管束植物叶片响应大气湿沉降氮的可能性.结果表明,法国梧桐叶片N%变化范围为1.48%~5.27%,均值为3.36%,根际土TN%为0.29%,叶片δ15N变化范围为4.48‰~8.39‰,均值为6.38‰.叶片N%与δ15N具有较好的相关性,随时间变化皆呈现春夏较高、秋季降低的趋势,冬季落叶,无监测数据.结合该采样点同期雨水监测数据,发现叶片N%与雨水中DIN浓度(0.57~6.74 mg.L-1)、叶片δ15N与雨水δ15NH4+-N呈现一致的变化规律,表明湿沉降氮是叶片吸收氮的一个重要来源,法国梧桐叶片指示大气N沉降量的变化成为可能.研究还发现法国梧桐叶片δ15N比其吸收氮的2个主要端元(根际土δ15TN:3.19‰±1.04‰,雨水δ15N-NH4+:-19.76‰~-10.41‰)都偏正,表明法国梧桐在吸收氮的过程中存在着较大的同位素分馏.
Leaves of Platanus orientalis were collected since Mar.2009 till Apr.2010,in an urban area at Guiyang.After mass of experiments and analysis,we carried out constructing the temporal variation of foliar N% and δ15N: both higher in Spring/Summer,lower in Autumn,no data of Winter because of leaf abscission.Results showed that foliar N% varied from 1.48% to 5.27%,with an annual average of 3.36%,while the average concentration of total N in rhizospheric soil was 0.29%.The foliar N% rose and fell relative to DIN in rainwater(range from 0.57 mg·L-1 to 6.74 mg·L-1),indicating that the N% content in foliar tissue of plant was approximately proportional to atmospheric N inputs.The range of foliar δ15N were from 4.48‰ to 8.39‰,with the average of 6.33‰,much higher than the δ15N-NH+4 of rain water(-19.76‰——10.41‰) and δ15TN of rhizospheric soil(3.19‰±1.04‰).Besides,a good uniform correlation between foliar δ15N and δ15N-NH+4of rain water were found.As synthesis of two main N sources,the more positive δ15N values of Platanus orientalis can be explained by isotopic fractionation during N uptake and basipetal translocation.These responses of both foliar N% and δ15N to atmospheric nitrogen deposition,revealed the potential value in using vascular leaves as bio-monitors for assessment of N deposition,furthermore,for prevention and control of air pollution in urban ecosystem.