PARENT SESSION
Poster Session #49: Elevated CO₂ II.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Effects of CO₂ enrichment on mycorrhizal responsiveness of tallgrass prairie species: an inverse relationship.

REYES, MELISSA^*,1, JOHNSON, NANCY¹, WOLF, JULIE¹, ¹ Northern Arizona University, Flagstaff, AZ

ABSTRACT- Anthropogenic enrichment of CO₂ is expected to influence plant communities and their associated mycorrhizae. We investigated the impacts of elevated atmospheric CO₂ on the mycorrhizal responsiveness (MR) of 14 prairie plants, including C-4 grasses, C-3 grasses, forbs and legumes. Each plant species was grown with and without arbuscular mycorrhizal (AM) inoculum at elevated or ambient CO₂ and each treatment was replicated within 6 different greenhouse chambers. At four-months, plant biomass and AM colonization were measured and MR was calculated ((biomass of +AM plants - biomass of - AM plants)/biomass of +AM plants). C-3 grasses were more responsive to CO₂ than C-4 grasses and C-3 forbs responded variably to CO₂. Across all plant species, CO₂ enrichment increased relative allocation to roots and AM fungi decreased it; however, individual plant species varied significantly in their responses. AM fungi consistently stunted C-3 grasses while other functional plant groups showed both positive and negative MR. We expected CO₂ enrichment to increase MR because AM benefits should increase as carbon becomes relatively less limiting and mineral nutrients become relatively more limiting. Instead, we observed that elevated CO₂ never increased MR, and in some species it decreased it. Species that benefited most from elevated CO₂ responded most negatively to AM fungi. This inverse relationship between plant responsiveness to elevated CO₂ and mycorrhizae is likely linked to plant carbon balance but the mechanism is not yet understood.

KEY WORDS: mycorrhizal responsiveness, CO2 enrichment, prairie plants, AM fungi