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