Nutrient stoichiometry and toxic nectar in Catalpa speciosa
Plants depend on soil to obtain mineral nutrients for plant growth and productivity. These mineral elements which are essential for normal plant growth can be divided into two categories, macronutrients or micronutrients. Macronutrients (N, P, K, Ca, Mg and S) are minerals needed in large quantities to ensure adequate plant growth, while micronutrients (B, Cu, Fe, Cl, Mn, Mo, and Zn) are only needed by the plant in small quantities (6). Since plants must acquire these nutrients, what happens if they are limited in supply? This concept is termed nutrient limitation, which refers to, “the limitation of productivity in an individual plant of monospecific strand because of an inadequate supply of an essential nutrient in the soil”. If this nutrient were increased in abundance, the plants overall productivity would increase as well (4). Thus, nutrients available in the soil play a key role in a plant’s overall ability to conduct physiological processes.
One of these physiological processes affected is the production of secondary metabolites. These metabolites are termed ‘secondary‘ due to their relatively low abundance within the plant. Although in low abundance, these compounds play a large role in plant adaptation to their environment, and can be broken up into three categories: phenolics, terpenes and steroids, and alkaloids (3,5). One important area of study involving these compounds that has yet to be fully explored is toxic nectar. Nectar is about 90% sugar, with the other 10% containing amino acids, lipids, antioxidants, mineral ions and secondary compounds (1). Phenolics and alkaloids have been identified as two of the secondary metabolites which give nectar its toxicity, mainly to “protect” the plant from nectar thieves (1,2).
Previous studies have shown that nutrient supply can affect the production of these secondary compounds. Waring et. al....