Modification of root morphological parameters and root architecture in seedlings of Fraxinus ornus L. and Spartium junceum L. growing on slopes

A computerised image analysis system was used to investigate several root morphological parameters in young seedlings of broom (Spartium junceum L.) and manna a (Fraxinus ornus L.) growing in three different environmental conditions: slope, terrace and plane. Data show that slope, to a greater extent than terrace, affects the root system of both species by increasing significantly the length and number of root apices of first-, second- and third-order lateral roots. Besides these variations in morphological parameters, the overall architecture of the root system results modified on a slope. In fact, an metrical distribution of lateral roots was observed around the tap root and along two main directions: up-slope and down-slope. The morphological parameters, analysed separately on the two portions of the root system, present significant differences. The following hypothesis is put forward: in response to a slope, the two species reinforce their anchorage strain by changing the organisation of the root system, particularly in the up-slope direction. In these two species, the occurrence of slight differences in response to a slope suggests that plant anchorage might require species-specific adaptations.