Spatio-temporal distribution of water and phosphorus determine growth of sorghum genotypes with contrasting nodal root angle

Abstract

Abstract Aims Increased subsoil water extraction through breeding of ‘designer’ root system architecture (RSA) may improve crop performance and resilience in the face of climate change (i.e. changing seasonal rainfall patterns). However, in many dryland environments, root systems face both water and nutrient scarcity (e.g. phosphorus (P)), with both resources often heterogeneously distributed in space and time. Under these conditions, interactions among RSA, nutrient distribution and soil water will determine crop performance, but remain poorly understood. Methods We grew two sorghum (Sorghum bicolor) genotypes defined by contrasting RSA (narrow or wide nodal root angle) in prepared soil cores with heterogeneous distributions of P and water along the soil profile. Plant growth and water use, shoot biomass, P uptake and root distribution were quantified in response to the different water × P combinations. Results Soil P placement and soil water distribution interactively determined plant growth and development in a genotype-dependent manner. The two sorghum genotypes shared common responses to P and water availability though varied for root and shoot traits and their relative responses to combined P and water stress. Conclusions Plant responses to the different water × P combinations were illustrative of the occurrence of spatio-temporal trade-offs between root architecture and efficient soil resource capture. The results suggest that the relative ability of crop root systems to effectively exploit soil profiles with greater resource availability will not necessarily be important for crop productivity in heterogeneous soil systems. Local environmental constraints should be considered when deploying genotypes with selected root architectural traits.