The growth of arbuscular mycorrhizal (AM) fungi is intimately linked to that of their plant hosts, because AM fungi are obligate biotrophs. Global change factors that affect plant communities (e.g., elevated carbon dioxide concentrations, warming, tropospheric ozone production) are thus also likely to affect AM fungi. The interactions of these factors and responses are complex and not well understood. Urbanization can serve as a surrogate to study the interaction of global change factors, because its effects parallel those of global change. The effects of urbanization also warrant study in their own right, as cities grow in area and population. We present the community and hyphal growth dynamics of AM fungi along a single urban-to-rural transect established in and around Baltimore, MD in 2002. Day and night air temperatures, soil temperatures, and carbon dioxide concentrations all increase from the rural to the urban end of the transect. Bulked topsoil and subsoil from a single agricultural site were separately placed into four plots each at rural, suburban, and urban sites along this transect. Plots are 2 x 2 m in area and 1.1 m deep. The imported soil is a Cordurus silt-loam with excessive N, P, and K. Five years after establishment of the plots, strongly divergent plant communities have emerged along this transect. We hypothesize that AM fungal communities are covarying with the plant communities and/or the temperature and carbon dioxide gradients. We also expect hyphal growth to vary along the transect, due to changes in growing season and carbon dynamics. Spores of AM fungi were extracted from samples taken in February 2006 as well as from trap cultures, and were identified visually at 400x magnification. Hyphae of AM fungi were extracted from repeat composite samples, composed of three smaller cores from each plot, and also quantified at 400x magnification.