Combining spring wheat genotypes with contrasting root traits 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 (“shallow root system” SRS and “deep root system” DRS) and their mixture at the booting stage. 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 traits. The SRS genotype had a higher fRWU than the DRS genotype in the topsoil and vice versa in the subsoil. In the mixture, both genotypes maintained complementary fRWU distributions and, in response to the water deficit, increased their contribution in subsoil by 0.5% cm −1 and decreased their contribution in topsoil by -1.2% cm −1 compared to the monoculture. This study introduces novel observations of root water uptake plasticity, which is determined by genotype root traits, soil water availability, and interactions with neighboring plant root traits. This study highlights the potential of contrasting root traits mixtures to improve their water and nutrient access facing water deficit.