How does variation in the active photosynthetic area affect the secretion of extrafloral nectar in Chamaecrista sp.?

Abstract

Plants secrete extrafloral nectar as an indirect defense against herbivores. One of the main factors modulating the costs related to the production of this nectar is the sunlight. The photosynthesis provides both the energy for the production of extrafloral nectaries and the carbohydrates alocated for the secretion of extraforal nectar. We know that the total photosynthetic rate of the plants is directly related to the active photosynthetic area of all its leaves. Yet, there are only a few studies that tried to quantitatively describe the relationship between plant photosynthetic area and the plant investment in extrafloral nectar. In this study, we will evaluate in which proportions the variation in the active photosynthetic area of plants bearing extrafloral nectaries influences the quantitative and qualitative characteristics of the extraforal nectar. For that, we will use as a model a species belonging to the genus Chamaecrista (Fabaceae). Species of Chamaecrista present extrafloral nectaries in the base of its leaves that are attended by several ant species. We will manipulate the active photosynthetic area of 30 plants and measure the photosynthetic rate and the volume and carbohydrates concentration of the extrafloral nectar secreted. We hypothesized that plants with larger active photosynthetic exhibit higher photosynthetic rates and, consequently, secrete more nectar with better quality than plants with lower photosynthetic areas. Our result may shed a new light on the physiological mechanisms driving temporal and spatial variation in the outcome of ant-plant interactions mediated by extrafloral nectar.