Plant diversity effects on soil microbes more pronounced at elevated [CO₂]. Microbial biomass (µg Cmic g-1 soil dry mass) and basal respiration (BR; µl O2 h-1 g-1 soil dry mass) as affected by plant species richness (SR) and CO₂ concentrations. Dashed lines indicate ambient CO₂ levels, solid lines elevated CO₂ levels (+180 ppm). SR x CO₂ for Cmic: p=0.007; SR x CO2 for BR: p=0.03). Data from August 2010. Means with SE. Redrawn after Eisenhauer et al. (2013).