The effect of moisture, nutrients and disturbance on storage organ size and persistence in temperate herbs

Abstract

1. Perennial herbaceous plants in seasonal temperate climates must form belowground storage organs to contain carbohydrates for seasonal regrowth and to mitigate disturbance and damage. The factors that dictate the size and turnover of these organs are still little understood. According to the Integrator-Splitter Hypothesis, storage organ persistence decreases with greater moisture and nutrient availability. The Resprouter-Seeder Hypothesis predicts that investments into storage organs are the largest when severe disturbances occur at an intermediate frequency. Additionally, according to the Carbon Surplus Hypothesis, storage organ size should increase with lower nutrient availability.2. We measured storage organ traits (lateral spread and persistence) and size parameters for more than 200 species of clonal perennial herbs and assessed their relationship with different environmental gradients linked to productivity (moisture and nutrients) and disturbance regime (disturbance frequency and severity).Additionally, we included plant height to account for potential scaling relationships between these traits and plant size. 3. Disturbance frequency had negative effects on storage organ size and turnover, other environmental parameters (moisture and disturbance severity) had positive effects. Storage organ volume correlated strongly with organ diameter and plant size (height).4. The divergence between lateral spread and persistence along the moisture gradient supported the Integrator-Splitter Hypothesis and reduction of volume and storage organ persistence under greater disturbance frequency supported the Resprouter-Seeder Hypothesis. Storage organ size was not affected by nutrient availability; thus our results contradict the Carbon Surplus Hypothesis. Although this is important evidence for plant allocation and storage strategy, future studies will need to include measurements of storage organ carbohydrate content to understand the difference in allocation between investment into structural growth as opposed to stored carbohydrates for later use.

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

“…Most data in those studies (e.g., Poorter et al, 2015) were obtained from short‐term experiments in which plants were established from seeds and rhizome biomass was thus small or not yet developed. Some species start to produce rhizomes only at the end of the first growing season or later (Klimešová, 1994; Niinemets, 2005) even when their lifespan can be up to decades (Bartušková et al, 2022). In the literature we surveyed, the two studies that recorded total biomass as well as root and rhizome biomass using plants grown from seed (Powelson and Lieffers, 1992; Wijte, 2005), the time from germination to harvest was 69 days and 119 days, respectively, typical of the short length of such studies that are not intended to report the biomass of plants that have reached the ontogenetic stage of reproducing.…”

“…Another mechanism is production of yearly rhizome increments of different length; as we know from analysis of rhizome volume, those parameters of rhizome growth are negatively correlated. Thus, plants with long‐lived persistent rhizomes have short rhizome increments, while short‐lived rhizomes are characterized by large increments (Bartušková et al, 2022), and both lead to limited accumulation of biomass in rhizomes.…”

“…We can expect that, according to this economic spectrum, short‐lived rhizomes will have a low amount of lignin but a high concentration of storage carbohydrates, while long‐lived rhizomes will have high concentrations of lignin and low concentrations of storage carbohydrates. The economic spectrum for rhizomes or other non‐acquisitive belowground organs was only recently considered (Lubbe et al, 2021; Bartušková et al, 2022), and short‐lived rhizomes with large lateral spread prefer wet and disturbed sites, while long‐lived rhizomes with short lateral spread are typical of dry and undisturbed places (Bartušková et al, 2022). With regards to their anatomical properties and carbohydrate concentration, we do not yet have enough information across species to support our speculations.…”

Trash or treasure: Rhizome conservation during drought

“…Both rhizome types vary greatly in their traits such as persistence of connection and lateral spread (Table 1; Bartušková et al, 2022).…”

“…While the rhizome grows and produces new increments (which may be branched to varying degrees), its older increments senesce and are lost at a rate specific for each species. The increment growth and senescence dynamics of rhizomes are expressed as persistence (Bartušková et al, 2022). The discarded part of the rhizome becomes part of the below‐ground litter that forms 33% of total annual litter in grasslands and 48% in forests (Freschet et al, 2013).…”