有机与非有机莴苣的氮稳定同位素辨识研究

为了证明利用氮稳定同位素技术鉴别有机蔬菜的可行性，本试验研究了不同肥料条件下土壤和莴苣不同部位的同位素特征变化情况。设置4个不同肥料条件：撒施有机肥（N 400 kg ? hm-2）、局部施尿素（N 300 kg ? hm-2）和撒施尿素（N 400 kg ? hm-2），以及对照（不施用任何肥料）。结果表明不同肥料条件下土壤15N丰度（即δ15N）差异显著（P 对照 > 局部施尿素 > 撒施尿素。各肥料条件下土壤δ15N值均呈现先升高再降低最后趋于平稳的变化规律，峰值出现在定植后20 d。不同处理莴苣δ15N值的差异及变化规律与土壤δ15N值变化规律相同。莴苣不同部位δ15N值比较结果为：外叶 > 根 > 内叶。莴苣内部同位素特征受环境影响最迅速。总体上，莴苣内叶和土壤的δ15N变化可以反映施肥情况，从而可对判断有机蔬菜种植过程中氮肥的施用种类提供依据。

Identification of Organic or Conventional Lettuce by Nitrogen Isotope

δ15N values of lettuce and soil were studied with different fertilizer conditions to prove the feasibility of using δ15N to discriminate between organic food and conventional food，4 treatments were laid out：Organic fertilizer in traditional broadcast way（N 400 kg ? hm-2），urea in partial fertilization way （N 300 kg ? hm-2），urea in traditional broadcast way（N 400 kg ? hm-2）and the control without fertilizer. The δ15N values of lettuce and soil in 4 treatment were significantly different（P control > urea in partial fertilization way > urea in traditional broadcast way. The temporal variations in the δ15N of lettuce and soils were similar among 4 treatments：Their δ15N values increased rapidly at first，then reduced slowly and stabilized finally. Maximum appeared in 20 days after transplanting. The δ15N value order of different lettuce organs is external part > root > internal part，and the difference is significantly（P < 0.05）. To sum up，the δ15N in inner of lettuce and soil can be used as a marker to reveal the history of nitrogen fertilization. It is useful tool for identifying the use of synthetic nitrogen fertilizer in the process of lettuce planting.