Abstract
Soil fungi are important components of terrestrial ecosystems. They function as decomposers, pathogens, parasites, and mutualistic symbionts. Their main mode of dispersal is to liberate spores into the atmosphere. In this study we tested the hypothesis that a higher atmospheric CO
2
concentration will induce greater sporulation in common soil fungi, leading to higher concentrations of fungal propagules in the atmosphere. In our field experiment, the concentration of airborne fungal propagules, mostly spores, increased fourfold under twice-ambient CO
2
concentrations. Analysis of decomposing leaf litter (likely the main source of airborne fungal propagules) indicated that the fungi produced fivefold more spores under elevated CO
2
. Our results provide evidence that elevations in atmospheric CO
2
concentration can directly affect microbial function, which may have important implications for litter decay, fungal dispersal, and human respiratory health. Key words: atmospheric CO
2
, fungal spores, global change, Populus tremuloides.