The Numerical Simulation Of Water And Nutrient Uptake By Plant Root

The water and nutrient uptake by plant is mainly taken by plant roots(zeroth and first order lateral), arbuscular mycorrhizal fungi(AMF) and root hairs and so on. The differences among the morphological and structural of plant root systems, soil environment and nutrition resources may lead to the discrepancy of water and nutrient uptake mechanism. Therefore, it is necessary to quantitatively take study on the roots take up water and nutrients in the agricultural production. This thesis primarily studies the differential equation models of water and nutrient uptake by the plant root system and effects of physiological parameters on water and nutrient uptake by the numerical simulation method. The thesis consists of three parts:In the first part, the single root takes up water from the axial and the radial pathways that are effected by the root internal pressure, while the pressure is de-termined by the ratio of the axial conductivity and the radial conductivity in the solution of the model. Because the axial and radial conductivity of the roots of the different plants is different, we consider the ratio of axial and radial conductivity of the primary and the lateral roots of Zea mays L., Agave Americana Linn, Opuntia stricta etc., and obtain the basic form of the solution of the root internal pressure. The results show when the ratio of the axial conductivity to the radial is small e-nough, the primary root pressure of crop is close to the pressure at the root base near the soil surface, the situation is apply to the primary root of Zea mays L. and Amygdalus persica L.; when the ratio of the axial conductivity to the radial is large enough, the pressure of the lateral crop is close to the water pressure in the soil, the situation is fit for plants, e.g., Citrus aurantium L., Poncirus trifoliata (L.) and Swingle Citrumelo.In the second part, the AMF can receive photosynthesis products from the plant, while mycorrhizas may offer water and nutrients to the host plant, they are the mutualistic symbiotic associations. We establish the model that we take the mycelium uptake as a sink term in the diffusion equation. This model is implied to study the influences of five parameters on the phosphate uptake of the AMF:the buffer power of soil, the water content of soil, the diffusion coefficient of phosphate, the initial phosphate concentration in the soil solution and the average radius of hyphal. The numerical results show that the buffer power of soil, the initial phos-phate concentration and the average radius of hyphal can promote the phosphate uptake of the AMF; the effect of the diffusion coefficient of phosphate and the water content of soil on phosphate uptake of the AMF in the model is insignificant; at the beginning of hyphas growth, the phosphate uptake of root is larger than the myceli-um, otherwise afterwards. In summary, the soil environment, nutrition resources and hyphal morphology codetermine the phosphate uptake by the mycelium.In the third part, based on the Kirk model, we divide the root zone into the root hair zone and domain outside the root hair zone, decribe the root surface and root hair phosphate uptake with the Michaclis-Mentcn kinetic, and take root hair uptake with a sink term in the diffusion equation. The improved model is used to investigate the effect of citrate exudation of the main root on phosphate uptake by the rice root system. The numerical results show that the phosphate concentration gradient dynamically develops within the root hair zone; the phosphate concentration in the soil solution of the improved model is belower than the Kirk model; at the beginning of the root hair growth, the phosphate uptake of root is larger than the root hair, the phosphate uptake of the hair root dominate the phosphate uptake after 16 hours. We proposed that citrate exudation of the main root and root morphology of the rice codetermine the influx of phosphate uptake by root system.