法国梧桐叶片氮含量及氮同位素对城市大气湿沉降氮的响应研究

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.

Platanus orientalis foliar N% and delta15 N responses to nitrogen of atmospheric wet deposition in urban area

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 delta15 N: 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 x L(-1) to 6.74 mg x L(-1)), indicating that the N% content in foliar tissue of plant was approximately proportional to atmospheric N inputs. The range of foliar delta15N were from 4.48 per thousand to 8.39 per thousand, with the average of 6.33 per thousand, much higher than the delta15N-NH4+ of rain water (-19.76 per thousand(-) -10.41 per thousand) and delta15TN of rhizospheric soil (3.19 per thousand +/- 1.04 per thousand). Besides, a good uniform correlation between foliar delta15N and delta15N-NH4+ of rain water were found. As synthesis of two main N sources, the more positive delta15N values of Platanus orientalis can be explained by isotopic fractionation during N uptake and basipetal translocation. These responses of both foliar N% and delta15N 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.