Glomalin-related soil protein in the rhizosphere of Robinia pseudoacacia L. seedlings under higher air temperature combined with Cd-contaminated soil

Glomalin-related soil protein (GRSP) can bind heavy metals and plays an important role in soil carbon sequestration. The GRSP contains glycoproteins produced by arbuscular mycorrhizal fungi (AMF), as well as lipids, humic materials and non-mycorrhizal-related heat-stable proteins, which might be affected by environmental conditions. Current and predicted changes in global climate make it important to understand how GRSP might be affected by higher atmospheric temperatures and heavy metal contamination of soil. Here, we investigated the response of GRSP to higher temperature in the rhizosphere of Robinia pseudoacacia L. seedlings in cadmium (Cd)-contaminated soil. Easily extractable (EE) and total (T) GRSP concentrations increased significantly (P<0.05) under Cd pollution alone. Compared with ambient temperature, a higher temperature (2.7 degrees C) alone significantly (P<0.05) increased EE- and T-GRSP concentrations, the EE-GRSP:T-GRSP ratio and the GRSP:soil organic carbon (SOC) ratio, but significantly (P<0.05) decreased SOC content in the rhizosphere. Higher temperature significantly (P<0.05) increased EE- and T-GRSP concentrations, the EE-GRSP:T-GRSP ratio and the GRSP:SOC ratio, but decreased SOC content under Cd pollution. Under higher temperature, the amount of Cd bound to GRSP increased significantly (P<0.05), and available Cd content decreased significantly (P<0.05). Glomalin-related soil protein contributed more carbon to the rhizosphere SOC pool under higher temperature+Cd than under Cd alone, and the higher temperature led to a significant (P<0.05) decrease in available Cd. Under the higher temperature, T-GRSP contributed more to the decrease in available Cd than did EE-GRSP. Increases in GRSP resulting from higher temperatures could increase Cd binding in contaminated soil.