Do root-sprouting and non-root-sprouting species differ in response to injury? Effect on growth, root buds and phytohormones

Root-sprouting (RS) clonal herbs are reported to be better adapted to severe disturbance than other clonal species, and their investments in clonal and storage organs are smaller than those in rhizomes. RS ability seems advantageous, so why is it not more common among plants? In a pot greenhouse experiment, we subjected two closely related clonal herbs differing in RS ability (RS Inula britannica and rhizomatous I. salicina) to severe biomass removal and looked for potential barriers to RS. We confirmed RS only in the already reported RS species I. britannica. However, RS was not boosted by disturbance in this RS species, i.e., the number of root buds and sprouts was not affected by biomass removal. Aerobic root respiration did not differ between the RS and non-RS species, and the phytohormone profiles differed significantly more between the RS and non-RS species than between the injured and non-injured individuals. The common hypothesis, however, never tested, that RS is facilitated by a low auxins to cytokinins content ratio was supported. Our results suggest that intrinsic phytohormone regulation is behind RS ability. Injury-causing phytohormonal imbalance seems to be less important, at least in spontaneously RS species such as I. britannica.