The role of deep roots in enhancing drought tolerance and nutrient uptake in diverse species and genotypes of grasses

Deep roots play a vital role in water and nutrient uptake and supply to assist in higher tolerance of increasing drought events under current global climate change scenarios. However, few studies have been made under field conditions to identify the differences between species and genotypes of grasses in root traits, water use efficiency (WUE), and nutrient uptake under drought stress. Stable isotope applications have revolutionized our understanding of water and nutrient dynamics in root systems, offering precise insights into plant resource uptake. In this study, experiments with grasses were done in a large-scale semi-field root phenotyping facility (RadiMax) equipped with rainout shelters to simulate drought conditions. In five experiments from 2016 to 2023, we measured the variations of root traits related to rooting depth among grass species and genotypes. The RadiMax facility enables the observation of root growth in up to 600 lines of diverse species and genotypes, with 150 to 300 lines being utilized in various grass experiments. Root traits were observed through minirhizotrons to more than 2 m depth and were quantified using an AI-based image analysis system (RootPainter). The RadiMax facility also allows deep placement of stable isotopes (²H and ¹⁵N), to be used as tracers for deep uptake by the root system. In this study, stable isotopic labelling was used in three studies from 2019 to 2023, in combination with the natural enrichment of ¹³C as a drought stress indicator. In this way, direct root phenotyping through minirhizotrons was combined with deep root function phenotyping based on the stable isotope measurements. Our preliminary results indicate that deep rooting will benefit plants as it contributes to deep water uptake under drought conditions, which indicates that selecting deep root traits should be included in the breeding of grass cultivars, to develop more drought-resilient genotypes.