By some estimates, as little as 1% of the original expanse of North America’s tallgrass prairie remains, and the survival of almost all grassland plants depends on the formation of the symbiotic partnership with arbuscular mycorrhizal (AM) fungi. The Central Great Plains also serves as the central migratory pathway for nearly half of North America’s monarch butterflies. With the loss of these grasslands, the monarch butterfly is currently experiencing severe declines in population. Monarch larvae are specialist herbivores, feeding exclusively on milkweed species along the regions of monarch distribution. Some milkweed species, such as common and butterfly milkweed, are highly dependent on AM fungi for survival. However, dependence on this symbiosis is not known for most milkweed species.
Our research was conducted at greenhouse facilities near Oklahoma State University, Stillwater, OK. Fifteen species of milkweed found throughout the Great Plains were selected to broadly assess the relative mycorrhizal responsiveness (rMR) of the genus Asclepias. All seedlings were grown in sterile soil collected from native prairie sites, and half of the plants were inoculated with 20 g-1 of whole prairie soil with intact microbial communities. End of season biomass of mycorrhizal and non-mycorrhizal plants was used to calculate rMR.
Results/Conclusions
rMR of selected milkweeds varied greatly between species, ranging from 38 to 91%. This was unexpected, based on previous research that has assessed dependence of various species of specific genera. However, all but one species of milkweed produced significantly greater (p ≤ 0.05) biomass when inoculated with whole prairie soil. This suggests that while there is remarkable variation within the genus, most species receive benefits from the association with AM fungi. Our study is the first to assess rMR of a wide variety of milkweed species, all of which are known to be consumed by monarch larvae. Current work is being conducted to determine percent mycorrhizal colonization of plant roots. Additionally, these results are being compared to milkweed phylogenies to determine if similar dependencies appear in the most closely-related individuals, or if environmental factors are determining dependency. Our research indicates planting milkweed for monarch habitat must include AM fungi for plant survival, and restoration success.