What is on the menu? Botanical carnivory in carnivorous plants of New England (USA)

Carnivorous plants obtain nutrients from arthropod prey (carnivory) and their environment. However, little is known about the seasonal diet shifts between carnivory versus environment nutrient acquisition among co-occurring carnivorous plant species. Although studies reporting captured prey species for carnivorous plants are abundant, studies investigating the composition of assimilated prey species are scarce. Here, we report spatiotemporal dynamics in carnivory versus environmental nutrient acquisition and compositional analysis of assimilated prey species for carnivorous plants of New England (USA). We measured the natural abundance stable isotope ratios of aquatic Utricularia inflata (Lentibulariaceae), terrestrial Sarracenia purpurea (Sarraceniaceae) and Drosera intermedia (Droseraceae) and their nutrient sources during their growing season in two oligotrophic ponds in New England (USA). MixSIAR, a Bayesian stable isotope mixing model, was used to estimate the extent of carnivory for each plant species and the composition of prey species assimilated in terrestrial carnivorous plants. Aquatic U. inflata acquired more nutrients from carnivory (c. 70%-100%) than terrestrial species (c. 30-60%). Sarracenia purpurea acquired nutrients mainly from Formicidae. The nutrient sources for D. intermedia varied spatiotemporally between arthropod species. The large contribution of carnivory to the nutrient budget of U. inflata could be due to its lack of roots and high metabolism. Sarracenia purpurea and D. intermedia could benefit from dissolved organic nitrogen in the environment. Our findings on prey compositions can be used as the first available prior information for the Bayesian approach in future studies. Understanding the sources of nutrients in carnivorous plants provides invaluable insight into their ecophysiology and may inform the conservation of their fragile wetland ecosystems.