Trait responses to AM fungi are stronger and more consistent than fixed differences among populations of Asclepias speciosa

Premise of the study: Arbuscular mycorrhizal (AM) fungi can promote plant growth and reproduction, but other plant physiological traits or traits that provide defense against herbivores can also be affected by AM fungi. However, whether responses of different traits to AM fungi are correlated, and whether these relationships vary among plants from different populations is unresolved. Methods: We assessed whether different populations of the perennial forb, Asclepias speciosa, grown from seed collected from different environmental conditions across its distributional range respond differently to AM fungi, and if the responses of six growth and defense traits are correlated. Key Results: Although there was strong genetic differentiation in mean trait values among populations, AM fungi consistently increased expression of most growth and defense traits across all populations. Responses of biomass and root:shoot ratio to AM fungi were positively correlated, suggesting that plants that are m...