Construction Costs, Payback Times, and the Leaf Economics of Carnivorous Plants

Abstract

Understanding how different and functional types "invest" carbon and nutrients is a major goal of plant ecologists. Two measures of such investments are "construction costs" (carbon needed to produce each gram of tissue) and associated "payback times" for photosynthesis to recover construction costs. These measurements integrate among traits used to assess leaf-trait relationship. Carnivorous plants are model systems for examining mechanisms of leaf-trait coordination, but no studies have measured simultaneously construction costs of carnivorous traps <i>and</i> their photosynthetic rates to determine payback times of traps. We measured mass-based construction costs (CC_mass) and photosynthesis (A_mass) for traps, leaves, roots, and rhizomes of 15 carnivorous plant species grown under greenhouse conditions. There were highly significant differences among species in CC_mass for each structure. Average CC_mass of carnivorous traps (1.14 +/- 0.24g glucose/g dry mass) was significantly lower than CC_mass of leaves of 267 non-carnivorous plant species (1.47 +/- 0.17), but all carnivorous plants examined had very low A_mass and thus, long payback times (495-1551 hours). Our results provide the first clear estimates of the <i>marginal</i> benefits of botanical carnivory, and locate carnivorous plants at the "slow and tough" end of the universal spectrum of leaf traits.