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Wheat proteins provide around 20% of all human dietary protein, but their end-use qualities are determined by the form and quantity of nitrogen in the endosperm. In the developed world, there is a heavy reliance in grain production on nitrogen supplied from synthetic fertilisers, and this fertiliser can contribute up to 50% of the on-farm emissions of greenhouse gasses in agriculture. However, despite increasing rates of application of synthetic nitrogen to cereals, wheat grain protein levels, in developed nations, have been frequently failing to reach the premium grade required by the bread-making market. Here, for the first time, we report that biological nitrogen fixation from a new generation of hardseeded annual forage legumes, when grown in rotation with cereal crops, can replace fertiliser N without compromising grain protein. The forage legumes were grown in rotation with Triticum aestivum, and compared with rotations that included a fallow, or a cereal crop at three rainfed sites in Western Australia with differing soil types for 2–4 years. The wheat received low, medium and high rates of urea to indicate if forage legumes can provide sufficient nitrogen for sustainable wheat production. At all sites and years studied, we discovered that cereal grains produced following a year of forage legumes had significantly higher protein levels than when grown as part of a continuous cereal rotation. These results were achieved in combination with a reduction in on-farm emissions (by over 200 kg/ha of CO2) without compromising yield as indicated by emissions accounting. Including appropriate forage legumes in farming systems allows production of low emission intensity grain proteins in dryland farming. [ABSTRACT FROM AUTHOR]

Global climate change with elevated atmospheric CO 2 concentrations and warming may potentially influence microbial function and nitrogen (N) cycling in various ecosystems. Despite the significance of diazotrophic mediation in soil N cycling within agricultural ecosystems, little is known about the impacts of climate change on diazotrophic abundance and community composition. An open-air field experiment growing wheat was conducted under four treatments: ambient condition (CK), CO 2 enrichment up to 500 ppm (CE), warming of canopy air by 2 °C over ambient (WA), and the combined CO 2 enrichment and canopy warming (CW). Quantitative real-time PCR and high-throughput pyrosequencing were used to analyze diazotrophic abundance and community composition in the bulk and rhizosphere soils. Results showed that both N 2 -fixation activity and nifH gene abundance were higher in the rhizosphere than those in bulk soil. N 2 -fixation activity and nifH gene abundance were significantly increased under elevated CO 2 treatments, while no significant change was observed under warming treatment. Elevated CO 2 levels altered the diazotrophic community composition and increased the alpha diversity. A redundancy analysis indicated that soil organic carbon, total nitrogen and available potassium were the most important factors in shaping diazotrophic communities in the wheat rhizosphere and bulk soil. These findings suggest that N 2 -fixation and diazotrophic community in wheat soil are more impacted by elevated CO 2 compared with warming. Therefore, understanding how simultaneous elevated CO 2 and temperature levels influences the microbial ecology of soil diazotrophs, can provide novel insights into the sustainability of agricultural production under future climate scenarios. • Elevated CO 2 increased N 2 fixation activity and nifH gene abundance. • Elevated CO 2 altered the diazotrophic community composition. • Elevated CO 2 increased the alpha diversity of diazotrophic community. • Warming alone had litter effects on diazotrophic communities. [ABSTRACT FROM AUTHOR]

Bradyrhizobium are N 2 -fixing microsymbionts of legumes with relevant applications in agricultural sustainability, and we investigated the phylogenetic relationships of conserved and symbiotic genes of 21 bradyrhizobial strains. The study included strains from Western Australia (WA), isolated from nodules of Glycine spp. the country is one genetic center for the genus and from nodules of other indigenous legumes grown in WA, and strains isolated from forage Glycine sp. grown in South Africa. The 16S rRNA phylogeny divided the strains in two superclades, of B. japonicum and B. elkanii , but with low discrimination among the species. The multilocus sequence analysis (MLSA) with four protein-coding housekeeping genes (dnaK , glnII , gyrB and recA) pointed out seven groups as putative new species, two within the B. japonicum , and five within the B. elkanii superclades. The remaining eleven strains showed higher similarity with six species, B. lupini , B. liaoningense , B. yuanmingense , B. subterraneum , B. brasilense and B. retamae. Phylogenetic analysis of the nodC symbiotic gene clustered 13 strains in three different symbiovars (sv. vignae, sv. genistearum and sv. retamae), while seven others might compose new symbiovars. The genetic profiles of the strains evaluated by BOX-PCR revealed high intra- and interspecific diversity. The results point out the high level of diversity still to be explored within the Bradyrhizobium genus, and further studies might confirm new species and symbiovars. [ABSTRACT FROM AUTHOR]

The genus Bradyrhizobium is considered as the probable ancestor lineage of all rhizobia, broadly spread in a variety of ecosystems and with remarkable diversity. A polyphasic study was performed to characterize and clarify the taxonomic position of eight bradyrhizobial strains isolated from indigenous legumes to Western Australia. As expected for the genus, the 16S rRNA gene sequences were highly conserved, but the results of multilocus sequence analysis with four housekeeping genes ( dnaK, glnII , gyrB and recA ) confirmed three new distinct clades including the following strains: (1) WSM 1744 T , WSM 1736 and WSM 1737; (2) WSM 1791 T and WSM 1742; and (3) WSM 1741 T , WSM 1735 and WSM 1790. The highest ANI values of the three groups in relation to the closest type strains were 92.4, 92.3 and 93.3 %, respectively, below the threshold of species circumscription. The digital DNA-DNA hybridization analysis also confirmed new species descriptions, with less than 52 % relatedness with the closest type strains. The phylogeny of the symbiotic gene nodC clustered the eight strains into the symbiovar retamae, together with seven Bradyrhizobium type strains, sharing from 94.2-98.1 % nucleotide identity (NI), and less than 88.7 % NI with other related strains and symbiovars. Morpho-physiological, phylogenetics, genomic and symbiotic traits were determined for the new groups and our data support the description of three new species, Bradyrhizobium archetypum sp. nov., Bradyrhizobium australiense sp. nov. and Bradyrhizobium murdochi sp. nov. , with WSM 1744 T (=CNPSo 4013 T =LMG 31646 T ), WSM 1791 T (=CNPSo 4014 T =LMG 31647 T ) and WSM 1741 T (=CNPSo 4020 T =LMG 31651 T ) designated as type strains, respectively.