Root phenes for improving nutrient capture in low-fertility environments

Issues surrounding soil fertility are fundamental to the productivity and sustainability of diverse agricultural production systems around the world. In developed economies, intensive fertilization is a chief economic, energetic, and environmental cost to crop production, depleting finite resources and causing massive pollution through leaching and runoff. In developing economies where access to, and utilization of soil amendments are rare, degraded soils with low nutrient availability are a primary constraint to yields. The most common challenges surrounding soil fertility in most production systems primarily involve nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), and zinc (Zn). A chief component of a robust and pragmatic solution to these soil fertility issues lies in the development of more nutrient-efficient crops. In pursuit of this objective, root phenotypes that improve the efficiency of soil exploration and acquisition of resources offer exceptional opportunities as breeding targets. Natural variation for root phenotypes can have significant effects on soil resource extraction by modifying the placement of roots in soil domains where limiting resources are most available, improving the metabolic efficiency of soil exploration, as well as altering the radial and axial transport of resources. In this chapter, we review root anatomical and architectural phenes that have demonstrated benefit for enhancing acquisition of the most commonly limiting nutrients, and advocate for the consideration of root phenotypes in breeding programs focused on developing crops with greater nutrient efficiency.