Ontogeny has a greater effect on defense and leaf nutritional status than fertilization in Stryphnodendron adstringens (Fabaceae)

Abstract

Investment of plants in defensive and leaf nutritional quality traits may vary with plant ontogeny and the availability of soil nutrients. In this study, we evaluated the effect of ontogeny and soil fertilization on leaf traits of the Brazilian cerrado tree Stryphnodendron adstringens (Fabaceae). Leaf defense traits (total phenolics, condensed and hydrolysable tannins, the number of extrafloral nectaries (EFNs) and the concentration of glucose, sucrose, fructose and total sugar in the extrafloral nectar) and leaf nutritional quality traits (water content, macronutrients, micronutrients and N:P and C:N ratios) were measured in 60 seedlings and 13 reproductive adults that grew in areas with previous P and Ca fertilization over eight years and in neighboring control plots in a Cerrado area in Distrito Federal, Brazil. Sampling was carried out three years after the last application of fertilizer. We found a strong effect of ontogeny on leaf traits: leaves of adult plants were more chemically defended and lower in nutritional quality than those of seedlings. Fertilization modified leaf nutritional quality traits in adults and seedlings, and defense traits in seedlings, increasing the number of EFNs on leaves, total phenolics and condensed tannins. In summary, adult plants of S. adstringens were poor in nutrients and invested more in phenolics and tannins than seedlings, all consistent with plant apparency theory. In contrast, seedlings were much more flexible in their defensive phenotype, with fertilization increasing allocation to total phenolics, condensed tannins and EFN production. This latter result suggests an ability of seedlings to take advantage of very local variation in resources that might increase the likelihood of surviving this vulnerable stage in the life cycle.