Non-structural carbohydrate accumulation and use in an understorey rain-forest shrub and relevance for the impact of leaf herbivory

1. Piper arieianum, an evergreen, understorey shrub of lowland moist forests of Central and South America, exhibits marked seasonal variation in reproductive activity even though climatic variation is low at the study site. Despite a lack of climatic seasonality, previous experimental leaf removal suggested that carbohydrate accumulation is seasonal, occurring prior to flowering.
2. We first tested the hypothesis that carbohydrates necessary for reproduction are accumulated prior to flowering, rather than during or after. By measuring non-structural carbohydrate production in the form of glucose and starch we found that the concentration of these reserves is greatest 1–3months before flowering, decreasing by 50% during peak fruit maturation.
3. The hypothesis that reproduction was the cause of this decrease in carbohydrate reserves was then tested by comparing reserves in plants that were prevented from flowering with those that flowered and produced fruit naturally. As predicted, reserves declined more in flowering than in non-flowering plants. A smaller decline in reserves of non-flowering plants was accompanied by greater stem and leaf production, suggesting that stored carbohydrates are also required for growth.
4. Because concentrations of non-structural carbohydrates were similar in roots, stems and leaves, and because the greatest amount of plant biomass is in stems for plants of a range of sizes, stems appear to be the main storage site of carbohydrate reserves in this plant species.
5. These results, together with previous studies, demonstrate that the impact of leaf herbivory on seed production in P. arieianum depends on the timing of that herbivory relative to the accumulation and use of non-structural carbohydrates.