Figure 1.

Conceptual overview illustrating relationships between pedoclimatic conditions and energy use efficiency of root growth. High bulk density and flooding decrease soil gas transport capacity, resulting in (i) decreased cellular oxygen concentration (p(O₂)) in the root growth zone and (ii) a shift from aerobic to anaerobic metabolism. Furthermore, high bulk density and drought increase soil penetration resistance, leading to higher mechanical stress at the growing root tip (σ(tip)). Energy requirements of root growth increase in response to low p(O₂) and high σ(tip), resulting in higher amounts of energy allocated to catabolic than anabolic processes and thus in a decrease of energy use efficiency.