Relationships between glomalin-related soil protein (GRSP) and soil organic carbon, total nitrogen or enzyme activity are unknown under the combined effects of varying daytime/nighttime elevated CO2 (eCO2) levels and arbuscular mycorrhizal fungi (AMF). We demonstrated that daytime, nighttime, and dual daytime/nighttime eCO2 levels could significantly increase AMF mycorrhization, soil organic carbon, total nitrogen, easily extractable, difficultly extractable and total GRSP in AMF soil. Under daytime eCO2, soil total nitrogen was significantly decreased in non-AMF soil, while mycorrhization alleviated soil nitrogen limitation. Nighttime and dual daytime/nighttime eCO2 significantly increased β-glucosidase and protease activities in AMF and non-AMF soils. With greater eCO2 effects in AMF than in non-AMF soils, GRSPs positively related to mycorrhization, soil organic carbon, total nitrogen, and β-glucosidase activity. Under the circumstance of global CO2 rising, besides mycorrhization, the combined effects of varying, non-steady-state daytime and nighttime eCO2, play important roles in soil carbon and nitrogen cycles.