Root gravitropism and below-ground competition among neighbouring plants: A modelling approach

Competition for nutrients among neighbouring roots occurs when their indivi dual depletion volumes overlap, causing a reduction in nutrient uptake. By exploring different spatial niches, plants with contrasting root architectu re may reduce the extent of competition among neighbouring root systems. Th e main objectives of this study were: (1) to evaluate the impact of root ar chitecture on competition for phosphorus among neighbouring plants; and (2) to compare the magnitude of competition among roots of the same plant irs. roots of neighbouring plants. SimRoot, a dynamic geometric model, was used to simulate common bean root growth and to compare the overlap of depletio n volumes. By varying the gravitropism of basal roots, we simulated three d istinct root architectures: shallow, intermediate and deep, corresponding t o observed genetic variation for root architecture in this species. Combina tions of roots having the same architecture resulted in more intense inter- plant competition. Among them, the deep-deep combination had the most inten se competition. Competition between deep root systems and shallow root syst ems was only half that of deep root systems competing with other deep root systems. Inter-plant root competition increased as soil diffusivity increas ed and the distance among plants decreased. In heterogeneous soils, co-loca lization of soil resources and roots was more important in determining reso urce uptake than inter-plant root competition. Competition among roots of t he same plant was three- to five-times greater than competition among roots of neighbouring plants. Genetic variation for root architecture in common bean may be related to adaptation to diverse competitive environments. (C) 2001 Annals of Botany Company.