Competition for plant nutrients in soil; a theoretical approach

Abstract

SummaryA mathematical model of whole plant growth in soil is presented. Particular emphasis is given to those factors which relate to the absorption of nutrients and water by the root system. There are two basic premises; that a plant is made up of two pools, structural material and precursors to structural material, and that structural material is produced by a reaction between a given ratio of precursors. The precursors are soluble carbohydrate and unbound nitrogen, probably nitrate. Increase in leaf area and root length is a consequence of absorbed nitrogen combining with photosynthate.The absorbing power and the distribution throughout the soil of the roots is controlled, through feedback mechanisms, by the ratio of the precursors, within the plant. The description of plant growth is interfaced with a model of one-dimensional flow of water and solutes in soil, and gives a model for investigating plant growth, or competition between root systems of more than one plant. The results of a number of simulations are presented. A sensitivity coefficient is defined to compare the effect of various properties on overall growth. Its value is calculated for 11 plant properties. It is some measure of the competitive advantage conferred on the plant by a change in the value of each property. The results of the competition experiments are given as replacement diagrams.The model has weaknesses. Because it is explicit, it defines in precise detail the experiments which would support the hypotheses, or suggest modifications to them. As a holistic analysis, it brings together ideas from different disciplines into one comprehensible framework.