Characterisation of the rhizosphere microbiota of Biserrula pelecinus L. across a two-season legume-cereal rotation

The drive to increase global agricultural production has focused attention on the potential for microorganisms to improve plant access to nutrition. The efficacy of these microbes depends on their ability to colonise and persist in the plant root environment, despite intense competition and shifts in community composition brought on by changes in season or host plant. In this study, we employed bacterial metabarcoding techniques in a simulated legume-cereal rotation to determine whether the host plants, namely the pasture legume Biserrula pelecinus L. (biserrula) and the wheat variety Triticum aestivum var. EGA Gregory, recruited a selective rhizosphere community and whether that community persisted across the rotation. The recruitment effect was strongest in biserrula after two consecutive seasons of growth, suggesting that conventional rotations may not allow adequate time for colonisation. In all, 21 taxa were identified as potential biserrula associates, including members of the Oxalobacteraceae and Rhizobiales. Additionally, biserrula may negatively curate its rhizosphere, reducing bacterial diversity. Microbial abundance increased between harvests, suggesting that seasonal effects may be significant in determining the community composition of the rhizosphere. These results were compared against a culture-dependent metabarcoding method, demonstrating that culturing yields microbial communities dominated by small cohorts of highly responsive taxa.