PARENT SESSION
Oral Session # 81: Soil Ecology II: Microorganisms and Mycorrhizae.
Presiding: SJ Hall
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 106.

Elevated atmospheric CO₂ and O₃ alter soil fungal community composition and function.

Chung, Haegeun ^*,1, Zak, Donald¹, ¹ University of Michigan, Ann Arbor, Michigan, U.S.A.

ABSTRACT- Atmospheric CO₂ and O₃ are rapidly rising due to human activity, and this change in atmospheric chemistry has the potential to alter the rate of carbon cycling in forest ecosystems. Changes in plant production and litter chemistry under elevated CO₂ and O₃ may alter microbial community composition and function because soil microorganisms are dependent on plant litter as a source of energy for heterotrophic metabolism. Because plant litter production is enhanced under elevated CO₂ and suppressed under elevated O₃, we hypothesized that microbial metabolism will increase under elevated CO₂ and decrease under elevated O₃; we also expected concomitant changes in microbial community composition. We tested our hypothesis at the Free-Air CO₂ and O₃ Enrichment (FACE) site in Rhinelander, Wisconsin, where Populus tremuloides, Betula papyrifera and Acer saccharum were grown under ambient and elevated CO₂ and O₃. We used extracellular enzyme analysis to measure microbial metabolism and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) to determine microbial community composition. The activity of hydrolytic enzymes that decompose cellulose and hemicellulose increased under elevated CO₂ and decreased under elevated O₃. These enzymes are produced mainly by fungi, and we observed clear shifts in fungal community composition under elevated CO₂ and O₃. We concluded that elevated CO₂ increases fungal metabolism and O₃ suppresses it, and this may be due to change in fungal community composition.

Key words: extracellular enzyme, carbon cycling, PCR-DGGE, fungal metabolism