Root traits and resource acquisition determining durum wheat performance under Mediterranean conditions: An integrative approach

Crop performance is very dependent on roots because they determine the capture of water and nutrients, and the crop’s subsequent growth and productivity. Durum wheat is a major crop in the Mediterranean region, where water and nitrogen availability limit its productivity. Therefore, the focus of this study was to uncover the response of root and shoot traits in durum wheat to different Mediterranean growing conditions and how they relate to better growth and yield performance. For this purpose, crop performance was evaluated in a set of modern durum wheat cultivars grown during four consecutive seasons and under contrasting water regimes, temperatures and nitrogen supplies, totalling 12 different growing conditions. Grain yield, biomass, other crop-growth traits (plant height, PH, and the Normalised Difference Vegetation Index, NDVI), together with physiological indicators of water (carbon isotope composition, δ13C, and canopy temperature depression, CTD) and nitrogen (nitrogen isotope composition, δ15N, and grain nitrogen yield, GNY) status were assessed. In addition, root architecture and distribution were measured using shovelomics and soil coring, and the provenance of the water captured by roots was determined by comparing the oxygen (δ18O) and hydrogen (δ2H) isotope compositions of water at the base of the stem, with water in different soil sections. Water and nitrogen status indicators combined with shovelomic traits allowed development of yield-prediction models. while higher yields were associated in most cases with better water status, root architecture was very responsive to different growing conditions. Overall, genotypes better adapted to rainfed conditions exhibited roots favouring deeper water extraction, whereas under support irrigation, the root system enabled water extraction from the topsoil as from deeper soil sections. Our study also highlights the limitation of shovelomics and soil coring as phenotyping approaches and proposes the δ18O of stem water as a promising functional phenotypic approach.

This study was supported by the Spanish Project PID2019- 106650RB-C2 from the Ministerio de Ciencia e Innovacion. ´ JLA acknowledges support from the Catalan Institution for Research and Advanced Studies, Generalitat de Catalunya, Spain, through its ICREA Academia program. FZR was a recipient of a research grant (FI-AGAUR) sponsored by the Agency for Management of University and Research Grants (AGAUR), in collaboration with the University of Barcelona. SCK was supported by the Ramon y Cajal RYC-2019-027818-I research fellowship from the Ministerio de Ciencia e Innovacion, ´ Spain. AGR was funded by a Margarita Salas post-doctoral contract from the Spanish Ministry of Universities affiliated with the Research Vice-Rector of the University of Barcelona. We thank members of the Integrative Crop Ecophysiology Group of the University of Barcelona and the personnel from the experimental station of ITACYL at Zamaduenas ˜ (Valladolid) for their assistance during the study’s data assessments. We extend our thanks to The Water Research Institute (IdRA) for their financial support to cover laboratory analyses. We thank Dr. J. Voltas from the University of Lleida, Spain, for his support with the δ18O and δ2 H water analyses.