Cadmium (Cd) and drought stresses are becoming dominant in a changing climate. This study explored the impact of Cd and Cd + drought stress on durum wheat grown in soil and sand at two Cd levels. The physiological parameters were studied using classical methods, while the root architecture was explored using non-invasive neutron computed tomography (NCT) for the first time. Under Cd + drought, all the gas exchange parameters were significantly affected, especially at 120 mg/kg Cd + drought. Elevated Cd was found in the sand-grown roots. We innovatively show the Cd stress impact on the wheat root volume and architecture, and the water distribution in the "root-growing media" was successfully visualized using NCT. Diverse and varying root architectures were observed for soil and sand under the Cd stress compared to the non-stress conditions, as revealed using NCT. The intrinsic structure of the growing medium was responsible for a variation in the water distribution pattern. This study demonstrated a pilot approach to use NCT for quantitative and in situ mapping of Cd stress on wheat roots and visualized the water dynamics in the rhizosphere. The physiological and NCT data provide valuable information to relate further to genetic information for the identification of Cd-resilient wheat varieties in the changing climate.
Keywords: cadmium; drought; gas exchange; neutron computed tomography; root architecture; wheat.