Abstract—

The natural nitrogen-15 abundance method does not always make it possible to calculate the rate of symbiotic nitrogen fixation by legumes and needs to be improved. Five legume species typical for the alpine belt of the Teberda Nature Reserve (Anthyllis vulneraria, Astragalus levieri, Hedysarum caucasicum, Oxytropis kubanensis, and Trifolium polyphyllum) have been grown from seeds under conditions of laboratory vegetation experiment. The results show that nodules on the roots of these plants are formed at early stages of their development; Trifolium polyphyllum does not form nodules either under high-mountain conditions or during growth in the laboratory. The natural ¹⁵N abundance in the leaves of legume plants in alpine ecosystems makes it possible to calculate the contribution of atmospheric N₂ to nitrogen nutrition as early as the first year of their development, while the isotopic nitrogen composition of the roots does not allow this parameter to be determined. The calculation of atmospheric nitrogen fixation rate should take into account isotope fractionation between symbiotic bacteria (nodules) and the host plant; otherwise, the proportion of fixed nitrogen in plant nutrition may be underestimated.

中文翻译：

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豆类植物在高山生态系统中的共生固氮作用：一项植被实验

摘要-

天然氮15丰度方法并不总是能够通过豆类来计算共生固氮率，因此有待改进。在实验室植被试验的条件下，已经从种子中生长了特伯达自然保护区的高山带典型的五种豆科植物物种（Anthyllis vulneraria，黄芪，Hedysarum caucasicum，Oxytropis kubanensis和Trifolium polyphyllum）。结果表明，这些植物根部的根瘤是在其发育的早期阶段形成的。多叶三叶草在高山条件下或实验室生长期间均不会形成结节。自然¹⁵高山生态系统中豆类植物叶片中的氮丰度，使得最早在其发育的第一年就可以计算大气中的N ₂对氮营养的贡献，而根部的同位素氮组成不允许将该参数设为决定。大气固氮率的计算应考虑共生细菌（结节）与寄主植物之间的同位素分馏；否则，固定氮在植物营养中的比例可能会被低估。