Responses of Drosera capensis and D. binata var. multifida (Droseraceae) to manipulations of insect availability and soil nutrient levels

Abstract

Nsectivory, growth, and nutrition of Drosera binata var. multifida and D. capensis were studied in long-established plantings in a green-house. Exclosures were used to manipulate insect availability to leaves, and substrate phosphorus and nitrogen fertiliser was added to increase these mineral nutrients. Neither species benefitted significantly from insect capture on a nutritional or energetic basis in nutrient-poor or -rich soils. However, both species benefitted from soil nutrient additions, and accumulated N and P in vegetative organs. Phosphorus levels in shoots were especially high in P fertilised plots for both species. In addition, P concentrations increased significantly in the roots of D. binata. Nitrogen levels in all tissues were slightly higher in N fertilised plots, and statistical differences were observed in roots of D. capensis and in shoots of D. binata. Drosera capensis showed increased growth with N and P additions, especially in root biomass. However, leaf number and rosette diameter increased where N and P were added together. This study adds to the growing evidence that insectivory is not as an important nutrient source to insectivorous plants, compared to inorganic soil-acquired nutrients, especially when the soil nutrient con-centrations are high. © 1993 Taylor & Francis Group, LLC.