用~(15)N天然丰度法估测结瘤作物的共生固N_2量

测定了位于北京西北郊的本所农场耕地及附近几个土样的土壤总Nδ15N值,农场耕地的δ15N值为6.39±0.42‰,本所庭园土壤为5.03±0.26‰,圆明园土壤为1.66±0.49‰。农场耕地土壤总Nδ15N的垂直变化为6.09±0.77～7.71±0.67‰,水平变化为6.52±0.55～7.13±0.73‰。 无N营养液砂培大豆的测定结果表明,根瘤富含15N,δ15N值为8.32±0.16‰和10.54±0.30‰,地上部贫化15N,δ15N为—2.25±0.48～—4.16±0.75‰,说明在固N2过程中和固N2产物输送转化过程中发生了N同位素的分馏,固N2分馏因数β=1.0023～1.0042。 用15N天然丰度法估计不同大豆品种的％Ndfa表明,不同大豆品种的N素自给能力不同。固N2植物的δ15N值明显低于非固N2植物的δ15N值,一般相差3～5δ15N,说明用15N天然丰度法评价这些植物的固N2状况是可能的。然而,不固N02植物也有较低的δ15N值,即便在同一地块上,非固N2植物的δ15N值也很不相同,有待进一步研究。

ESTIMATION OF SYMBIOTIC DINITROGEN FIXATION BY MODULATING PLANTS USING VARIATION IN NATURAL ~(15)N ABUNDANCE

Samples were collected from Institute farming field and some site near by. δ15N values of total soil N was 6.39±0.42‰5% for Institute farming field, 5.03±0.26‰ for garden of the Institute, 1.66±0.49‰ for Yuanminyuan park. δ15N value for total soil N in Institute farming field varied between 6.09±7.71‰ vertically, and between 6.52-7.13‰ horizontally.In an experiment conducted for measuring δ15N value of different parts of soybean, which was grown hydroponically in N-free medium, nodules enriched with 15N and δ15N value was 10. 54 ±0. 30‰. Aboveground parts delepted 15N. δ15N values were between -2.25±0.48-4.1 6±075‰, which indicated that fractionatiou occured in the course of dinitrogen fixation and transportation of N2 products. β value for soybean was 1.0023-1.0042.%Ndfa for different soybean cultivars was estimated by natural 15N abundance method.It showed that supportability-self was different for different cultivars.Measurement for other plants, especially for herbs, δ15N values for N2-fixing plants were much lower than that for non-N2-fixing plants.Generally, this difference was between 3-5 δ15N units. It is suggested that we could estimated dinitrogen fixation by natural 15N abundance method.However,some plants without ability to fix nitrogen from air, had lower δ15N value, and the δ15N value of non-N2-fixing plants, even though grown in the same site, were different apparently.These problems would be studied further.