A mathematical model of root uptake of cations incorporating root turnover, distribution within the plant, and recycling of absorbed species

Understanding the movement of cations in soil, particularly trace metals, i s required in many applications such as phytoremediation and pollution cont rol. A dynamic mechanistic model has been developed to describe the long-te rm root uptake of a surface-applied, strongly adsorbed, pollutant metal cat ion, such as radiocaesium, from soil. It consists of two submodels. The fir st calculates uptake per unit root length at a local scale over a root's li fetime, for various initial conditions. The second calculates cumulative up take at a whole-plant scale for the entire rooting depth as a function of t ime. The model takes into account the renewal of roots which are considered to have a limited lifetime. Root density may be a function of soil depth a nd a proportion of roots need not contribute to uptake. Recycling from deca ying, or grazed, roots and shoots is considered. Simulations show that removal of cations from soil is exaggerated unless so me recycling by roots or shoots is considered or the entire root length doe s not contribute to uptake. Because of root turnover, uptake is not rapidly limited by diffusive flux of the cation from the bulk soil solution to the solution-root interface. Uptake is very sensitive to root architecture and plant physiology.