Elevated ambient carbon dioxide and Trichoderma inoculum could enhance cadmium uptake of Lolium perenne explained by changes of soil pH, cadmium availability and microbial biomass

Trichoderma inoculum may mediate plant growth and uptake of heavy metals, but the combined effects and the mechanisms of Trichoderma sp. and elevated ambient carbon dioxide (CO2) on the cadmium (Cd) availability and plant uptake are far less investigated. A pot experiment was conducted to investigate plant growth, Cd uptake, and chemical and microbial biomass characteristics of the rhizosphere of Lolium perenne grown on three Cd-contaminated soils under combined effects of elevated ambient CO2 and Trichoderma virens strain F7 inoculum. Rhizosphere soil samples were analyzed for pH, concentrations of available Cd measured by diffusive gradients in thin-films (DGT-Cd) and microbial biomass carbon and nitrogen. It was found that the elevated ambient CO2 and Trichoderma inoculation, in combination or alone, significantly promoted plant biomass and total Cd uptake by plants with decreased soil pH (by 0.08-0.32 units) and increased microbial biomass carbon (by 21.54-121.21%) and nitrogen (by 21.88-112.95%) in the rhizosphere. Also, the concentration of DGT-Cd in the rhizosphere under elevated ambient CO2 and Trichoderma inoculum treatments was increased by 15.45-152.48%, indicating that there was more available Cd for plant uptake under effects of elevated ambient CO2 and Trichoderma inoculum. Results suggested that the acidulated rhizosphere, enhanced microbial activities and increased Cd availability may have contributed to the efficiency of plants in Cd accumulation under effects of elevated ambient CO2 and Trichoderma inoculum. (C) 2014 Elsevier B.V. All rights reserved.