Resource dynamics and plant growth: A self-assembling model for individuals, populations and communities

1. We describe a new model of plant growth that is general, deterministic, non-stationary and mechanistic in nature. Its purpose is to investigate the extent to which the morphology and function of the whole plant can be determined by resource acquisition and utilization on the part of its components. 2. The model is a two-dimensional section, showing the plant in its above- and below-ground environments. The whole plant is represented by a branching structure made up from standard 'modules'. The behaviour of the complete plant is determined exclusively by a rule set that acts only at the level of the individual module. 3. At the level of the whole plant, the model displays a classic S-shaped growth curve, plasticity in root-shoot allocation, and foraging in heterogeneous environments. 4. At the level of the plant population, the model exhibits self-thinning along a -2/1 self-thinning line. This accords with the behaviour expected of a two-dimensional system and also adds weight to the 'geometric' interpretation of the -3/2 self-thinning Line commonly seen in crowded populations of real plants. 5. An imposed 'mutation' in one of the modular rules allows us to produce a modified plant type that displays active foraging. In a set of simulations involving a model community containing both the modified and standard plant types, the modified type predominates in resource-rich environments, and vice versa. 6. The simulations demonstrate the effectiveness of modular rule-based methods from which whole-plant behaviour can arise as an emergent property. The model suggests that active foraging carries a cost that cannot satisfactorily be borne at low levels of resource availability. It also implies that competition for resources, both above and below ground is in the form of a 'contest' (rather than a 'scramble'). The success of the modular model highlights the primacy of resource acquisition and utilization in determining the ecological status of the plant.