Root growth and development do not directly relate to shoot morphogenetic strategies in temperate forage legumes

Abstract

Little is yet known about the component traits that control the deployment of root architecture in most grassland species. The aim of this study was to compare patterns of root growth in contrasting forage legumes and to analyse their dependency to shoot development. The parameters of a dynamic simulation model were identified for seven contrasting species in a series of greenhouse experiments in order to characterize root elongation, root branching and taproot growth. The model allowed us to explore the interactions between root development and whole plant growth. Most of the root morphogenetic parameters studied displayed significant inter-specific variability. Several traits appeared to be correlated, indicating a close association between extreme root tip diameters, the branching ability of roots and their maximal elongation rate. The species differed along two PCA axes which accounted respectively for the branching ability of fine roots and taproot development. Quite remarkably, the group of species identified for root development did not coincide with those previously identified for shoots, suggesting a degree of independence between the morphogenetic traits that control shoot and root architecture. However, both plant parts remained tightly linked through the trophic relationship represented by root biomass allocation. Our results suggest that the concomitant analysis of root and shoot development is necessary to properly decipher rooting strategies in forage legumes.