ABSTRACT

The natural abundance technique is used to estimate the amount of N fixed by a legume, but the B value of this particular species has to be known first. This value, however, varies with the rhizobium strains and climatic conditions. To assess this variation range for forage legumes growing under Uruguayan conditions, seeds of Lotus corniculatus L., Trifolium repens L. and Trifolium pratense L. were sown in pots containing vermiculite-sand and inoculated with a commercial or a promissory rhizobium strain, and grown in a greenhouse during the winter and spring, or in a growth chamber that simulated summer temperatures. At harvest, B values were determined by analyzing δ¹⁵N in shoots, and their proportion of N derived from air (%Ndfa) were also estimated. All B values were within the reported ranges. The rhizobium strain affected B only in L. corniculatus, resulting in a 0.55‰ shift between the commercial and the research strains. The growing seasonal effect, however, was important across the three species, with B values becoming more negatives as the temperature and the isotopic fractionation increased. However, the impact of these B value changes on the associated %Ndfa values were not always agronomically relevant, but depended on the particular legume–rhizobia combination.

摘要

自然丰度技术用于估计豆类固定的 N 量，但必须首先知道该特定物种的 B 值。然而，该值随根瘤菌菌株和气候条件而变化。为了评估在乌拉圭条件下生长的豆科牧草的这种变化范围，将小花莲、白三叶和三叶草的种子播种在含有蛭石砂的盆中，并接种商业或承诺根瘤菌菌株，然后生长在冬季和春季的温室中，或在模拟夏季温度的生长室中。在收获时，通过分析 δ ¹⁵确定 B 值还估计了芽中的 N，以及它们从空气中提取的 N 的比例 (%Ndfa)。所有 B 值都在报告的范围内。的根瘤菌菌株仅在受影响的乙L.百脉，导致在商业和研究菌株之间的0.55‰移。然而，季节性效应在这三个物种中很重要，随着温度和同位素分馏的增加，B 值变得更加负值。然而，这些 B 值变化对相关 %Ndfa 值的影响并不总是与农艺相关，而是取决于特定的豆科植物 - 根瘤菌组合。