Natural abundance of 15N of N derived from the atmosphere by different strains of Bradyrhizobium in symbiosis with soybean plants

EnglishTo quantify the BNF contribution to legumes using the 15N natural abundance technique, it is important to know the abundance of 15N of the plants grown entirely dependent on BNF (value ‘B’). The aim of the study was to determine the 15N natural abundance of N2 fixed by different Bradyrhizobium strains in symbiosis with one soybean cultivar. Treatments consisted of soybean plants cultivated with and without inoculation with ten Bradyrhizobium strains, in five replicates planted in Leonard jars in a sand/vermiculite mixture. Plants were harvested after 46 days. The ‘B’ values of the aerial tissue (‘Bs ’) ranged from -2.6 to -3.9 ‰. There was a tendency for the ‘Bs ’ values of plants inoculated with strains of B. elkanii to be more negative than plants inoculated with other strains. All ‘B’ values of the whole plant were less than 1 unit of δ15N (‰) different from zero, suggesting that the symbioses have little tendency to show significant isotopic fractionation during N2 fixation, but there is considerable depletion in 15N of the N translocated to the shoot tissue. portuguesPara quantificar a FBN em leguminosas, atraves da tecnica de abundância natural de 15N, e importante conhecer a abundância de 15N da planta leguminosa crescida inteiramente dependente da FBN (valor ‘B’). O objetivo deste estudo foi determinar a abundância natural de 15N do N2 fixado por diferentes estirpes de Bradyrhizobium em simbiose com uma cultivar de soja. Os tratamentos consistiram de plantas cultivadas sem e com inoculacao com dez estirpes de Bradyrhizobium, em cinco repeticoes. Foram utilizados vasos de Leonard, substrato de areia e vermiculita. As plantas foram colhidas apos 46 dias. Os valores de ‘B’ parte aerea (‘Bpa’) variaram entre -2.6 to -3.9 ‰. Houve tendencia para a abundância de 15N dos valores de ‘Bpa’ das plantas inoculadas com estirpes de B. elkanii a serem mais negativos que as plantas inoculadas com as outras estirpes. Todos os valores de ‘B’ da planta inteira foram menos de 1 unidade de δ15N (‰) diferente de zero, sugerindo que as simbioses tem pouca tendencia de mostrar fracionamento isotopico significativo, mas houve consideravel empobrecimento do isotopo 15N no N translocado a parte aerea