Growth and micronutrients distribution in Cichorium intybus L. - Funneliformis mosseae mycorrhizal symbiosis

It has been shown that arbuscular mycorrhizal (AM) fungi (AMF), symbionts living in close association with the root system of most land plants, can improve host nutrition and health, boost both primary and secondary plant metabolism and eventually enhance biomass production. In optimal growth conditions, mycorrhizal symbioses increase plant photosynthetic activity, thanks to the higher availability of nutrients. However, if the beneficial effects of the mycorrhizal symbiosis are known, nutrient exchange mechanisms occurring in fungal-plant relationships are not fully understood. This for at least two main reasons: 1) the experimental constraints involved in in vivo studies of nutrient transfer during the symbiosis, 2) the analytical limits in the investigation on the absorption and transfer of nutrients by fungal extraradical hyphal networks. With the aim of studying micronutrients distribution in mycorrhizal symbioses, chicory (Chichorium intybus L.) plants inoculated with Funneliformis mosseae IMA1 were analysed. The plants were maintained for one month in a growth chamber, in a quartz substrate enriched with a standard nutrient solution (Long-Ashton) in controlled conditions (25-21°C day/night temperature, 16:8-h light/dark cycle, 350 ?mol m-2 s-1 photosynthetic photon flux density). Iron (Fe), copper (Cu), zinc (Zn) and manganese (Mn) content and uptake were assessed in plants (shoots and roots) and in the extraradical mycelium (ERM) by Atomic Absorption (Varian SpectrAA model 220FS) and Inductively Coupled Plasma-Optical Emission (ICP-OES, Varian 720; LOD: 5-20 ?g L-1, LOQ: 20-40 ?g L-1) spectrophotometry. Mycorrhizal plants increased their total biomass, as revealed by the enhanced number and area of leaves. Zn concentration and content were higher in the shoots of mycorrhizal plants, while Fe accumulated mainly in roots. In the ERM, Fe, Mn and Zn amounts were larger than those of Cu. The leaves of mycorrhizal host-plants showed higher total carotenoid levels, with an increase of the carotenoid to chlorophylls ratio. Mycorrhizal symbiosis seems to improve Fe uptake through the extraradical network. The analysis of nutrient distribution patterns in plants and extraradical mycelium may provide important information on the ability of mycorrhizal mycelium to uptake and transfer key micronutrients to the host plant, useful for AMF application in food plant biofortification or bioremediation of polluted soils.