Relating root structure and anatomy to whole-plant functioning in 14 herbaceous Mediterranean species

This study investigated the relationships between root structure and anatomy and whole-plant functioning in herbaceous species. Fourteen annual and perennial species representative of a Mediterranean old-field succession were grown in monocultures in a common-garden experiment. Whole-plant functioning was assessed by inherent relative growth rate (RGR(max)), measured in standardized conditions, and maximum height (H-max). Root tissue density (TMDr), considered as a major component of root structure, was measured on roots harvested within in-growth cores. Anatomical characteristics were analysed on cross-sectional areas (CSA). TMDr was correlated positively with H-max and negatively with RGR(max). Root CSA explained interspecific variation in H-max but not that in TMDr and RGR(max). Root xylem CSA and xylem proportion in root CSA were positively correlated with TMDr and H-max and negatively with RGR(max). Mean xylem vessel CSA did not account for variations in TMDr, H-max and RGR(max). These results suggested that RGR(max) and H-max are constrained by opposite root structural and anatomical traits, which have potential links with hydraulic conductance, support and longevity.