We examined the response of mycorrhizal fungi to free-air CO 2 enrichment (FACE) and nitrogen (N) fertilization in a warm temperate forest to better understand potential influences over plant nutrient uptake and soil carbon (C) storage. In particular, we hypothesized that mycorrhizal fungi and glomalin would become more prevalent under elevated CO 2 but decrease under N fertilization. In addition, we predicted that N fertilization would mitigate any positive effects of elevated CO 2 on mycorrhizal abundance. Overall, we observed a 14% increase in ectomycorrhizal (ECM) root colonization under CO 2 enrichment, which implies that elevated CO 2 results in greater C investments in these fungi. Arbuscular mycorrhizal (AM) hyphal length and glomalin stocks did not respond substantially to CO 2 enrichment, and effects of CO 2 on AM root colonization varied by date. Nitrogen effects on AM fungi were not consistent with our hypothesis, as we found an increase in AM colonization under N fertilization. Lastly, neither glomalin concentrations nor ECM colonization responded significantly to N fertilization or to an N-by-CO 2 interaction. A longer duration of N fertilization may be required to detect effects on these parameters.