Figure 1.

Steep, Cheap, and Deep and Topsoil Foraging ideotypes in maize (top) and common bean (bottom) at 42 days after germination as simulated by opensimroot. The center image represents standard phenotypes in maize and common bean germplasm. In maize (representing a non‐tillering monocot root architecture), the Steep, Cheap, and Deep phenotype was generated by reducing the number of axial roots, decreasing lateral root branching density, and increasing the steepness of crown root growth angles, whereas the Topsoil Foraging phenotype was generated by doing the opposite. In common bean (representing an annual dicot root architecture), the Steep, Cheap, and Deep phenotype was generated by reducing the number of hypocotyl‐borne roots, reducing the number of basal root whorls, decreasing lateral root branching density, and increasing the steepness of basal root growth angles, whereas the Topsoil Foraging phenotype was generated by doing the opposite. It has been proposed that the Steep, Cheap, and Deep phenotype is useful for the capture of subsoil resources including water and leached nitrate, whereas the Topsoil Foraging phenotype is useful for the capture of topsoil resources including recently mineralized NO₃, NH₄, P, K, Ca, and Mg and, in some cases, micronutrient metals. Model parameters are based on empirical observations. Images courtesy of Ernst Schafer. Reproduced from Lynch (2019).