Branching patterns of root systems: comparison of monocotyledonous and dicotyledonous species.

BACKGROUND AND AIMS: Acropetal root branching is a major process which increases the number of growing tips and distributes their growth potential within the whole root system.

METHODS: Using a method presented in a recent paper, the defined branching traits were estimated in 140 different species, and the branching patterns of monocots (45 species) and dicots (95 species) were compared.

KEY RESULTS: It was checked that the method also applied to monocots (not considered in the previous paper), and that all traits could be estimated in each species. Variations of most traits were even larger for monocots than for dicots. Systematic differences appeared between these two groups: monocots tended to have a larger range in apical diameters (stronger heterorhizy), with both finer and thicker roots; the diameters of their lateral roots were also more variable; their roots exerted a stronger dominance over lateral branches. Altogether, species exhibited two main dependencies among their traits that were illustrated using two axes: (1) the 'fineness-density' axis separated the species which develop very fine roots and branch densely, from species without fine roots which space out their branches; and (2) the 'dominance-heterorhizy' axis separated the species according to the range in their apical diameter which was positively correlated to the level of dominance of mother roots over their branches. Both axes and correlations were remarkably similar for monocots and dicots.

CONCLUSIONS: Beyond the overall typology, this study went on to validate the phenotyping method in Natura, and showed its potential to characterize the differences in groups of species.