Abstract
Plants acquire soil P through root morphology, root physiology or symbiosis with arbuscular mycorrhizal fungi(AMF), their interplay being still poorly understood. We investigated how durum wheat belowground traitsrespond to AMF inoculation under varying soil P availability. Ten durum wheat varieties were grown in agreenhouse experiment, under optimal and limiting soil P levels, with or without inoculation of an AMFcommunity. Roots of 7-week old plants were collected to evaluate AMF colonization rates, root morphologicaltraits and rhizosphere phosphatase activities. Shoot biomass and shoot P uptake were quantified. Mycorrhizalgrowth response (MGR) was calculated. Principal Component Analysis was used to evaluate AMF-induced rootplasticity based on belowground traits, and mixed models were performed to assess the impact of soil Pavailability, durum wheat variety and AMF inoculation on these traits. AMF inoculation revealed the plasticityof root morphological traits: it resulted in increased Root Tissue Density (RTD), decreased Specific Root Length(SRL) and proportion of fine roots, while soil P availability had a lesser effect. Amongst durum wheat varieties,MGR varied from neutral to negative and was negatively correlated with AMF colonization rates, especiallyunder limiting soil P level. Durum wheat varieties exhibiting the highest AMF-induced root plasticity alsodisplayed the most negative MGR. Negative effect of AMF on both bread and durum wheat response havealready been observed. Our results suggest that AMF-induced root plasticity partially trigger these negativeresponses, and question about the symbiosis with AMF as a beneficial adaptative strategy for the studieddurum wheat varieties