Two isolates of Rhizophagus irregularis select different strategies for improving plants phosphorus uptake at moderate soil P availability

Abstract

The roots of most terrestrial plants form symbioses with a diversity of arbuscular mycorrhizal (AM) fungi, which make substantial contributions to plant phosphorus (P) uptake. Large genetic variation exists within AM fungi of the same species. However, the impact of these variations, on the mycorrhizal contribution to plants' P uptake by different isolates of the same species and the differences in physiological mechanism remain unknown. In the present study, we selected maize (genotype Oh 43) as the host plant and investigated the response of plant P uptake and soil organic P use efficiency to two different AM fungal isolates, Rhizophagus irregularis MUCL 41833 and R. irregularis MUCL 43194 at three soil P availability levels (10.3, 18.6, 43.3 mg kg−1, representing low, medium and high soil available P level, respectively). We found that at the medium soil available P level, R. irregularis MUCL 41833 produced large amounts of extraradical hyphae to explore soil and induced greater expression of phosphate transporter gene ZmPHT1;6 involved in the mycorrhizal pathway. While, R. irregularis MUCL 43194 recruited a specific, and different, bacterial community in the rhizosphere compared to R. irregularis MUCL 41833. This shift in rhizosphere microbiome was characterized by the recruitment of a greater abundance of Betaproteobacteriales when the plant was colonized by R. irregularis MUCL 43194, which showed a strong positive correlation with alkaline phosphatase activity, and suggested a link to greater organic P mineralization. Collectively, our results suggest that the two isolates of R. irregularis have different strategies for improving plant P uptake at the medium soil available P level, which deepened our understanding on the contribution and complexity of the mycorrhizal pathway to plant P uptake.