Leaf production, chemical defense, and maintenance costs for tropical rain forest shrub.
McHenry, Rendie *,2, Dyer, Lee 1, Chambers, Jeff1, Fincher, Malia1, 2 Dillard University, New Orleans, LA, USA1 Ecology and Evolutionary Biology, New Orleans, LA, USA
ABSTRACT- Quantifying the costs of plant chemical defenses has been difficult for ecologists, but it is an important component of understanding how plants respond to variation in biotic and abiotic inputs. The ant plant, Piper cenocladum, has been a useful system for indirectly demonstrating costs of chemical defenses. The concentrations of defensive amides in this plant were much lower when predatory ants were present, presumably to reduce costs of amide production. The concentration of plant secondary compounds also increased significantly with enhanced light and nutrient availability but was unaffected by herbivory. At a much larger scale (ecosystem versus organismal) in a central Amazon forest we found that the proportion of total carbon allocation to production of woody tissues varied as a function of growth rate from zero (no tissue growth, all allocation to maintenance respiration costs) to almost 80% for the fastest growing trees. A combination of these approaches, nutrient manipulation followed by quantification of defenses and measurement of production respiration, will allow for a quantitative measure of costs of chemical defense. We developed methods for quantifying costs of defensive amides in Piper species grown in greenhouses in a gradient of nutrient availability. The methods consist of determining leaf carbon construction and maintenance costs in individual plants under different soil nutrient availability treatments that generate variation in leaf-level chemical defenses. For Piper plants, costs are quantified as negative parameter estimates (from multiple regression) for amide concentration as a predictor of leaf tissue growth, maintenance respiration, and leaf toughness. This novel method contributes significantly to understanding the effects of resource availability on chemical defenses and herbivory.
Key words: Piper cenocladum
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.