Winter wheat phenotyping for deep root growth and function, reduced water stress and increased uptake of deep N and water

Background and Aims Deep roots may help plants adapt to climate change by allowing them to access deeper soil layers where water is still available, reducing water stress and increasing nitrogen (N) uptake. Water stress significantly affects yield during later developmental stages, but methods are lacking for phenotyping for deep rooting under field conditions and at maturity. Methods Over three years, we used minirhizotron root imaging in the RadiMax semi-field facility to compare deep rooting in winter wheat genotypes grown in field soil to 2.7m depth. We related this to deep soil uptake of water and N using isotopic tracers injected into the soil at 1.6-1.8m depth. Carbon isotope discrimination was used to evaluate water stress levels. Key results Deep rooting was positively correlated with uptake of deep-placed N and water, and uptake of deep placed N was three times higher in the genotype with deepest roots compared to the shallowest. Deep rooting was negatively correlated with water stress, measured using carbon isotope discrimination. This correlation was strongest in 2023, a dry year, highlighting the role of deep roots in mitigating water stress. Some genotypes had consistently deeper or shallower roots over the three experimental years, and there were strong correlations of isotopic measurements between genotypes across years. Conclusions Our findings show strong relationships between deep rooting and deep root functions, which indicate that deep rooting is a desirable trait which should be targeted. The significant genotypic variation observed, which can be phenotyped for even under field conditions, indicates that deep rooting is a trait that can be incorporated into breeding programs. Furthermore, the methods used in this study are effective and should be developed for further application.