PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Elevated CO₂ increases sporocarp production and intraradicle sporulation of one AMF species at Biosphere 2.

Wolf, Julie^*,1, Murthy, Ramesh ², Barron-Gafford, Greg², ¹ Northern Arizona University, Flagstaff, AZ, USA² Columbia University's Biosphere 2 Center, Oracle, AZ, USA

ABSTRACT- We quantified the growth of arbuscular mycorrhizal fungi (AMF) within the Intensive Forestry Mesocosm (IFM) at Biosphere 2 (Oracle, AZ, USA). The IFM is permanently partitioned into three bays, within which atmospheric carbon dioxide (CO₂) has been maintained at concentrations of 420, 800, or 1200 parts per million since 2000. From 2000 to 2002, ninety-four cottonwoods of similar genotype and age (all started from cuttings in 1998) were grown under the CO₂ concentrations within the three bays. In 2002, multiple soil and root samples were taken from each bay and combined, so that one composite sample represented a thorough spatial sampling of the area within each bay. Spores of the same six species of AMF were present in all three bays. Spore abundances of five of these species were similar in all three bays, but the sixth species (an unidentified Glomus species, producing Sclerocystis-type sporocarps), was increasingly abundant under increased CO₂ concentrations (9, 11, and 16 sporocarps per 100 g soil under 420, 800, and 1200 parts per million, respectively). The size of the sporocarps did not vary with CO₂ treatments. This pattern corroborates the findings of the two other studies in which AMF spore communities were quantified under elevated CO₂; in both, spores of certain species within the genus Glomus were more abundant under high CO₂ while the other species present did not change in abundance. A qualitative change in sporulation was also observed under the elevated CO₂ treatments at Biosphere 2. Sporocarps of the above-mentioned Glomus species, which are normally found in bulk soil, were also observed inside live roots growing under elevated CO₂ (0, 0.25, and 2.5 intraradicle sporocarps per 100 g soil at 420, 800, and 1200 parts per million, respectively). There is no previous documentation of sporocarps of this type developing intraradically. These quantitative and qualitative changes in sporulation provide further evidence that elevated CO₂ has important species-specific effects on arbuscular mycorrhizal fungi. These effects may impact plant and soil communities.

Key words: arbuscular mycorrhizal fungi, Biosphere 2 Center, elevated carbon dioxide, soil community composition