Combining spring wheat genotypes with contrasting root architectures for a better use of water resources in soil? Evidence from column-scale water stable isotopic experiments

Background and Aims The advantages of genotype mixtures on soil water balance are still poorly understood. We aim to determine the impact of soil water conditions (well-watered or chronic water deficit) on the root water uptake (RWU) of two contrasting root genotypes and their mixture at the booting stage. Methods We conducted a controlled plant-soil column experiment and quantified daily vertical profiles of the fraction of RWU (fRWU, % cm ^− 1 ), i.e. the relative contribution of RWU normalized by the thickness of each layer. This calculation was achieved by applying Bayesian modelling on non-destructive soil and transpiration water stable isotopic measurements after pulse labelling. We compared these results to the monitored plant soil water status, plant physiology and root architectures. Results The "shallow-rooted" genotype exhibited a greater fRWU compared to the "deep-rooted" genotype in the topsoil (3.87 ± 1.05 and 3.49 ± 1.05% cm ^− 1 , respectively) and vice-versa for the subsoil (resp. 1.16 ± 0.17 and 1.53 ± 0.41% cm ^− 1 ). The relative water uptake of all plant modalities from subsoil (+ 0.5% cm ^− 1 ) and topsoil (+ 0.29% cm ^− 1 ) increased under water deficit conditions. The genotype mixture maintained individual complementary fRWU distribution but shifted their contributions toward the subsoil (+ 0.5% cm ^− 1 ) and decreased those from the topsoil (-1.2% cm ^− 1 ) under water deficit. Conclusion This study introduces novel observations of root water uptake plasticity, which is determined by genotype root architectures, soil water availability, and interactions with neighboring plant root architectures. This study highlights the potential of contrasting root architectures mixtures to improve their water - and nutrient – access facing water deficit.