Most land plants form the ancient arbuscular mycorrhizal (AM) symbiosis, while carnivory is a younger trait that evolved in several angiosperm orders. The two biotic interactions similarly help plants acquire mineral nutrients, raising the question of whether they can coexist. However, the mycorrhizal status of carnivorous plants has long remained speculative. We surveyed the occurrence of AM-associated genes across carnivorous plant lineages, performed AM fungal inoculation assays, and microscopically evaluated the patterns of colonization. We found convergent losses of the AM trait either coincident with or predating the emergence of carnivory. Exceptionally, the carnivorous plant Roridula gorgonias retains symbiosis-related genes and forms arbuscules. The youngest carnivorous lineage, Brocchinia reducta, showed signatures of the early stages of AM trait loss. An AM-associated CHITINASE gene encodes a digestive enzyme in the carnivorous plant Cephalotus, suggesting gene cooption. We uncovered a mutually exclusive trend of AM symbiosis and carnivory, with only rare instances of coexistence. These findings illuminate the largely unexplored processes by which plant nutritional strategies evolve and supplant one another over time.
Photo: Brocchinia reducta growing on Mt. Roraima in the Guiana Highlands (photo by Andreas Fleischmann)
