Arbuscular mycorrhizal fungi-mediated biologically fixed N transfer from Vachellia seyal to Sporobolus robustus

This study aimed to investigate the role of arbuscular mycorrhizal (AM) fungi on biological N fixation in Vachellia seyal and transfer of fixed N-2 from V. seyal to intercropped Sporobolus robustus under greenhouse conditions. Both plants were grown individually in pots to prevent root contact ("Solid barrier" treatment) or together in two-compartment containers delimited by a plexiglass plate with holes either covered with a 30 mu m nylon mesh allowing only hyphal connections between plant roots ("Mesh barrier" treatment), or without nylon mesh allowing hyphae and roots to intermingle ("No barrier" treatment) in a low-nutrient soil. Both plant species were inoculated with the AM fungal Rhizophagus irregularis IR27 strain ("Myc+" treatment) or not inoculated ("Myc-" treatment), whereas all V. seyal seedlings were inoculated with a rhizobial strain Ensifer sp. LCM 4579 ("Nod+" treatment). The (15) N isotope dilution method was used to determine the amount and proportion of atmospheric N fixed by V. seyal (%Ndfa) and the total fixed N that was transferred to intercropped S. robustus. Mycorrhizal inoculation factor had a significantly effect on plant growth parameters and shoot N concentration in V. seyal, but not in S. robustus. The estimated proportions of N fixed by V. seyal was higher in Myc + treatment (65%) than in Myc- treatment (42%) as well as for the amount of fixed N. About 14% of fixed N were transferred to S. robustus from AM fungal links, whereas N transfer via exudation plus transfer through mycorrhizal network reached 19.5%. The implications of these results are discussed.