The position along rhizome as a surrogate for root age: effect on fine root traits

Fine root morphology underlies the resource acquisition strategy of species, yet its development during root lifespan remains underexplored. Focusing on rhizomatous herbs, a promising system for root ontogeny research, we used root position along the rhizome as a proxy of root age and asked: how much do root traits differ between young and old fine roots?

We collected whole clonal fragments of 19 temperate eudicot herbaceous species in Czechia, central Europe, always at two localities (per species) differing in moisture. We measured fine root morphological traits (in old and young parts of rhizomes), rhizome traits and above-ground biomass.

Root tissue density increased and specific root length decreased with fine root age in the studied species. Fine root diameter showed no overall change in response to root age but increased with root age in plants with longer rhizomes, possibly owing to greater age variation along longer rhizomes. The changes in fine root traits were small in magnitude in comparison to between-species differences in trait values and were not affected by site moisture or nutrient status.

Our results suggest that fine root traits change during root lifespan, shifting towards higher root tissue density, larger diameter and smaller specific root length. This can lead to local trait variation within a single root system, possibly affecting small-scale processes, such as below-ground competition. On the level of species, this variation is relatively small and thus need not be reflected in root sampling methods.