Herbs are not just small plants: What biomass allocation to rhizomes tells us about differences between trees and herbs

Abstract

Premise: Biomass accumulation over years in vertical stems of trees leads to hypoallometric scaling between stem and leaf biomass within this growth form, while for herbaceous species, biomass allocation between these organ types typically exhibits isometry. However, biomass accumulation in herbs can occur in belowground perennating organs (e.g., rhizomes) that are, contrary to aboveground parts of herbs, long-lived. Although ecologically important, biomass allocation and accumulation in rhizomes (and similar organs) have mostly not been studied. Methods: We assembled data on biomass investments into plant organs for 111 rhizomatous herbs based on a literature survey and greenhouse experiment. We estimated the proportion of whole-plant biomass invested into rhizomes and, using allometric relationships, analyzed scaling between rhizome and leaf biomass and whether it is more variable than for other organs. Results: On average, rhizomes comprise 30.2% of the total plant biomass. The proportion allocated to rhizomes does not change with plant size. Scaling between rhizome and leaf biomass is isometric, and allocation to rhizomes is not more variable than allocation to other organs. Conclusions: Rhizomatous herbs accumulate substantial biomass in rhizomes, and rhizome biomass scales isometrically with leaves, contrary to the hypoallometric relationship between stem and leaves in trees. This difference suggests that the rhizome biomass is in balance with aboveground biomass-a resource of carbon for rhizome formation that, at the same time, is dependent on carbon stored in rhizomes for its seasonal regrowth.

Belowground morphology as a clue for plant response to disturbance and productivity in a temperate flora

“…Productivity implies the role of BGFs in the carbon economy of plants. It has recently been shown that clonal growth organs can contain a large proportion of total plant carbon (Harris et al ., 2023) and that their building represents a significant carbon sink, namely for young plants (Martínková et al ., 2020). The presented results support these findings on a much larger set of species and habitats.…”

“…While coarse roots are ubiquitous, clonal organs such as rhizomes or bulbs are especially common in herbs and shrubs, and may constitute a large part of their overall biomass. For example, belowground rhizomes may form 30% of herb total biomass because they are perennial and thus can accumulate over years, in contrast to aboveground herbaceous plant parts (Harris et al ., 2023). These organs and their belowground position must have some important function in plant life because plants have various adaptations to place them belowground or to position them horizontally at the soil surface.…”