Arbuscular Mycorrhizal Fungi Improve Rice Production in Zinc-Amended Soils by Altering Zinc Transport and Translocation Routes.

Abstract

Human activities including industry and overcultivation resulted in marginal soils, unbalanced in nutrients or polluted with heavy metals. Zinc (Zn) is an essential micronutrient and its nonoptimal soil bio-availability, negatively affects plant growth and production. Arbuscular mycorrhizal fungi (AMF) could improve Zn acquisition in limited conditions and prevent accumulation in plant tissue in contaminated soils. However, it is not clear how AMF impact host plant Zn uptake and transport routes. In this study we assessed the potential of commercial AMF inoculum to support rice growth and production in non-Zn-fertilised, Zn-fertilised and Zn-polluted soils alongside their impact on host plant nutrient balances and Zn uptake and translocation routes. The results demonstrated that AMF inoculation restores rice growth and grain production in Zn-amended soils and that Zn amendment improves root colonisation. Shoot ionomes were particularly sensitive to differences in Zn supply and differentially affected in AMF and mock-inoculated plants. When present in excess, AMF inoculation decreased accumulation of Zn in shoots and disturbed Zn-P (phosphorus) relationship. We could not detect a mycorrhiza-specific Zn transporter in rice but rather a modification of expression for Zn transporters in the direct uptake routes. AMF inoculation interacts with the Zn-dependent response of heavy metal ATPase (OsHMA) transporters involved in root-to-shoot translocation. All together, these data indicate a change in relative importance of different direct Zn transport routes upon AMF colonisation. These findings provide valuable insights into how AMF symbiosis influences Zn uptake and distribution in rice under varying Zn conditions, allowing for the development of plant-fungus bioremediation and biofortification technologies.