Variations in glomalin-related soil protein in Vicia faba rhizosphere depending upon interactions among mycorrhization, daytime and/or nighttime elevated CO₂ levels

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.