The influence of slope on Spartium junceum root system: morphological, anatomical and biomechanical adaptation

Root systemshave a pivotal role in plant anchorage and their mechanical interactions with the soil may contribute to soil reinforcement and stabilization of slide-prone slopes. In order to understand the responses of root systemto mechanical stress induced by slope, samples of Spartiumjunceum L., growing in slopeand in plane natural conditions, were compared in their morphology, biomechanical properties and anatomical features. Soils sampled in slopeand plane revealed similar characteristics, with the exception of organic matter content and penetrometerresistance, both higher in slope. Slopesignificantly influenced root morphology and in particular the distribution of lateral rootsalong the soil depth. Indeed, first-order lateral rootsof plants growing on slopecondition showed an asymmetric distribution between up- and down- slope. Contrarily, this asymmetric distribution was not observed in plants growing in plane. The tensile strength was higher in lateral rootsgrowing up- slopeand in plane conditions than in those growing down- slope. Anatomical investigations revealed that, while roots grown up- slopehad higher area covered by xylemfibers, the ratio of xylemand phloem fibers to root diameter did not differ among the three conditions, as also, no differences were found for xylemfiber cell wall thickness. Roots growing up- slopewere the main contributors to anchorage properties, which included higher strength and higher number of fibers in the xylematic tissues. Results suggested that a combination of root-specific morphological, anatomical and biomechanical traits, determines anchorage functions in slopeconditions.