Arbuscular mycorrhizal fungi can reduce the bioavailability of Zn and Fe in the grain of barley (Hordeum vulgare) and oat (Avena sativa)

Oat (Avena sativa) and barley (Hordeum vulgare) are increasingly being grown and consumed for their ‘functional food’ properties, but they also accumulate large amounts of stored phosphorus (P) as phytic acid (PA) in the seed, leading to reduced zinc (Zn) and iron (Fe) bioavailability. Arbuscular mycorrhizal (AM) fungi in the soil colonise the roots of oat and barley and can provide an additional source for P, Zn, and Fe, but their effect on the bioavailability of Zn and Fe is not known. We grew six varieties each of oat and barley, and either amended the soil with P fertiliser or not, then inoculated with a commercial source of the AM fungus Rhizophagus irregularis, or not. In both crops, AM fungal inoculation and P fertiliser each increased the accumulation of PA. While the bioavailability of Fe in oat was reduced by AM fungal inoculation, Zn was unaffected. In barley, Zn bioavailability was reduced with AM fungi, but Fe bioavailability was unaffected. The bioavailability of Zn and Fe in both oat and barley was extremely low. Both crops store luxury P as PA rather than converting it to grain, so micronutrient bioavailability in oat and barley is highly dependent on mycorrhizal contribution of Zn and Fe.