Root metabolic costs including respiration are a significant limitation to soil exploration and therefore soil resource acquisition. Root traits that reduce the metabolic cost of soil exploration may therefore have adaptive value in conditions of drought and suboptimal nutrient availability, and may enhance N capture in leaching environments. Architectural traits may reduce root metabolic costs by reducing inter-root competition and by allocating root foraging effort to spatiotemporal domains that optimize the relationship between root metabolic investment and soil resource capture. Anatomical traits can reduce the metabolic burden of maintaining root tissue. Examples will be presented in which phenotypic variation in maize for root architectural and anatomical traits that affect root system respiration is associated with improved water capture from drying soil and improved N capture from low N soil.