Plant root systems have two key functions: they acquire water and nutrients and transport them to aboveground plant parts. As a single root segment cannot be fully efficient at both functions, plants face a trade-off in optimising whole-root-system functioning which is largely unexplored in herbs. Clonal growth, being common in herbs and widespread over the angiosperm phylogeny, offers an alternative transport pathway via horizontal stems, while adventitious roots formed on these stems shorten the transport distance from roots to leaves. I thus hypothesise that clonal growth allows for a higher acquisition efficiency of root systems. To test this hypothesis, I will apply a novel comparative experimental approach using pairs of phylogenetically related species differing in the extent of clonal growth. The main comparative test will be preceded by method optimisation and complemented by experimental manipulation of two model clonal species to estimate phenotypic plasticity of root functions. To investigate the acquisition-transport trade-off in root systems, I will combine an ecophysiological approach of stable isotope labelling to estimate acquisition efficiency with root morphology and anatomy to provide mechanistic insights. I will integrate my experience in plant clonality and stable isotope labelling with the host's deep knowledge of root functional traits. The project aims to establish methods to study root acquisition vs. transport in herbs of different growth forms and to determine the cross-organ belowground functional diversity and root phenotypic plasticity that underpins the ability of species to adjust to different environmental conditions. The results will significantly contribute to our understanding of basic principles of plant functions hidden belowground. Those functions, related mechanisms and consequences are fundamental to ecology, plant physiology and agriculture, and relevant to increasing drought and nutrient enrichment under global change.