Rice root properties for internal aeration and efficient nutrient acquisition in submerged soil

• The characteristics of Oryza sativa roots required for internal aeration may conflict with those for efficient nutrient acquisition, particularly the surface area available for absorbing nutrients and the extent of oxygenation of the rhizosphere. • A model was developed for calculating the steady-state diffusion of O₂ through a primary root and its laterals and the simultaneous consumption of O₂ in respiration and loss to the soil. Results for a realistic set of parameter values were compared with available experimental data, and a sensitivity analysis given. • It was seen that a system of coarse, aerenchmymatous, primary roots with gas-impermeable walls conducting O₂ to short, fine, gas-permeable laterals (i.e. the basic architecture of current rice genotypes) provided the greatest absorbing surface per unit aerated root mass. • With this architecture and typical rates of root respiration, rates of O₂ loss to the soil can be sufficient to, for example, nitrify sufficient NH₄ ⁺ to NO₃ ⁻ to allow a plant to absorb half its N as NO₃ ⁻ , as well as to oxidize toxins such as Fe²⁺ .