Mapping macro and micronutrients in leaves of wheat colonized by intact arbuscular mycorrhiza extraradical mycelium through Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS)

Arbuscular mycorrhizal fungi (AMF) are obligate symbionts of over 80% of land plants. A mutualistic relation that grants colonized plants privileged access to water, nutrients and protection against biotic and abiotic stress. However, their use in intensive agriculture has been limited as result of an incomplete understanding of the complex ecological dynamics that drive plant–microbe interactions. Under Mn toxicity, in acidic soils, the development of an intact AMF extraradical mycelium (ERM) by stress-adapted native plants (Developers), can promote earlier AMF colonization, increased growth and protection against metal toxicity in the subsequent crop. In a previous study, the ERM developed from Ornithopus compressus (ORN) more than doubled wheat shoot weight and increased P contents while decreasing toxic shoot Mn. This beneficial effect was promoted by ORN-mediated soil microbial enrichment, which selected the AMF that colonized the succeeding wheat crop. The biochemical mechanisms promoting improved wheat growth are not yet fully understood but may involve the enzymatic management of oxidative stress and subcellular redistribution of nutrients and of excess Mn. In the present work, shoot Ca, Fe, Mg, Mn, P, K, Si, Na and Zn were mapped through Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), in wheat grown for 3 weeks in undisturbed soil where ORN previously developed an extensive ERM network. Element mapping allowed the detection of higher levels of Fe, Mg, Mn, P, K, Na and Zn in the interveinal parts of wheat leaves while Ca and Si showed higher levels in vascular zones in the adaxial leaf side. This preliminary work is part of an ongoing project which aims at identifying biochemical mechanisms responsible for the protective properties of an early AM colonization of crops by ERM previously developed in association with native plants under Mn toxicity. Future research will determine the subcellular apoplastic or symplastic location of these elements as well as of excess Mn.