Root Gravitropism and Below-ground Competition among Neighbouring Plants: A Modelling Approach

Competition for nutrients among neighbouring roots occurs whentheir individual depletion volumes overlap, causing a reductionin nutrient uptake. By exploring different spatial niches, plantswith contrasting root architecture may reduce the extent ofcompetition among neighbouring root systems. The main objectivesof this study were: (1) to evaluate the impact of root architectureon competition for phosphorus among neighbouring plants; and(2) to compare the magnitude of competition among roots of thesame plant vs. roots of neighbouring plants. SimRoot, a dynamicgeometric model, was used to simulate common bean root growthand to compare the overlap of depletion volumes. By varyingthe gravitropism of basal roots, we simulated three distinctroot architectures: shallow, intermediate and deep, correspondingto observed genetic variation for root architecture in thisspecies. Combinations of roots having the same architectureresulted in more intense inter-plant competition. Among them,the deep-deep combination had the most intense competition.Competition between deep root systems and shallow root systemswas only half that of deep root systems competing with otherdeep root systems. Inter-plant root competition increased assoil diffusivity increased and the distance among plants decreased.In heterogeneous soils, co-localization of soil resources androots was more important in determining resource uptake thaninter-plant root competition. Competition among roots of thesame plant was three- to five-times greater than competitionamong roots of neighbouring plants. Genetic variation for rootarchitecture in common bean may be related to adaptation todiverse competitive environments. Copyright 2001 Annals of BotanyCompany Root architecture, phosphorus, competition, common bean, Phaseolus vulgaris L. nutrient uptake, gravitropism