Bradyrhizobium strain and the 15N natural abundance quantification of biological N2 fixation in soybean

Abstract

In commercial plantations of soybean in both the Southern and the Cerrado regions, contributions from biological nitrogen fixation (BNF) are generally proportionately high. When using the 15 N natural abundance technique to quantify BNF inputs, it is essential to determine, with accuracy, the 15 N abundance of the N derived from BNF (the 'B' value). This study aimed to determine the effect of four recommended strains of Bradyrhizobium spp. (two B. japonicum and two B. elkanii) on the 'B' value of soybean grown in pots in an open field using an equation based on the determination of d 15 N natural abundance in a non-labelled soil, and estimate of the contribution of BNF derived from the use of 15 N-isotope dilution in soils enriched with 15 N. To evaluate N 2 fixation by soybean, three non-N 2 -fixing reference crops were grown under the same conditions. Regardless of Bradyrhizobium strain, no differences were observed in dry matter, nodule weight and total N between labelled and non-labelled soil. The N 2 fixation of the soybeans grown in the two soil conditions were similar. The mean 'B' values of the soybeans inoculated with the B. japonicum strains were -1.84 ‰ and -0.50 ‰, while those inoculated with B. elkanii were -3.67 ‰ and -1.0 ‰, for the shoot tissue and the whole plant, respectively. Finally, the 'B' value for the soybean crop varied considerably in function of the inoculated Bradyrhizobium strain, being most important when only the shoot tissue was utilised to estimate the proportion of N in the plant derived from N 2 fixation. 15 N, e estimativas da contribuição da FBN derivado do uso da técnica de diluição isotópica de 15 N em solo enriquecido com 15 N. Para avaliar a fixação de N 2 pela soja três plantas referenciam foram crescidas nas mesmas condições. Independente da estirpe de Bradyrhizobium, não foi observada diferença para matéria seca, massa de nódulos e N total entre solo marcado e não marcado. A fixação de N 2 em soja crescida nas duas condições de marcação do solo foi semelhante. Os valores médios de 'B' para plantas de soja inoculadas com estirpes de B. japonicum foram, em média, de -1,84 ‰ e -0,50 ‰ enquanto as inoculadas com B. elkanii apresentaram médias de -3,67 ‰ e -1,00 ‰, para parte aérea e planta inteira, respectivamente. Finalmente, o valor 'B' para a cultura da soja variou consideravelmente em função da estirpe de Bradyrhizobium inoculada, sendo mais importante quando se utiliza somente a parte aérea da planta para estimar a proporção do N da planta derivado da fixação de N 2 . Palavras-chave: Bradyrhizobium elkanii, Bradyrhizobium japonicum, Glycine max, valor de 'B' Biological N 2 fixation in soybean 517

Crop rotation biomass and arbuscular mycorrhizal fungi effects on sugarcane yield

“…A large proportion of the N present in soybeans usually comes from BNF. Guimarães et al (2008) found that 96% of the N present in above ground parts of soybeans were derived from BNF, values which are in agreement with those obtained by Perin et al (2006) for sunn hemp. However, in the present study, only about 27% of the N present in the soybean residues were from BNF (Table 5), probably because of poor specific population of fixing bacteria for soybeans in the experimental site, which have been grown with sugarcane for long time.…”

Crop Rotation Biomass and Effects on Sugarcane Yield in Brazil

“…A large proportion of the N present in soybeans usually comes from BNF. Guimarães [33] found that 96% of the N present in above ground parts of soybeans were derived from BNF, values which are in agreement with those obtained by [32] for sunn hemp. However, in the present study, only about 27% of the N present in the soybean residues were from BNF (Table 5), probably because of poor specific population of fixing bacteria for soybeans in the experimental site, which have been grown with sugarcane for long time.…”

Diversity of Nitrogen-Fixing Bacteria Associated with Switchgrass in the Native Tallgrass Prairie of Northern Oklahoma

“…Within this group, 58% of the sequences were related to nifH in bacteria from the order Rhizobiales and were present in all sample types. More specifically, these sequences were affiliated with the genera Bradyrhizobium, Mesorhizobium, Methylobacterium, Rhizobium, and Sinorhizobium, all of which contain species that are known to fix nitrogen in symbioses with legumes (38)(39)(40)(41)(42)(43)(44)(45).…”