Soil respiration and microbial activity in a Mediterranean grassland exposed to Free Air CO 2 Enrichment (FACE)

The effects of elevated atmospheric CO 2 on in situ soil respiration and belowground biomass were studied in a FACE (Free Air CO 2 Enrichment) facility. A Mediterranean grassland community was exposed to elevated and ambient CO 2 concentrations in a mini-FACE system in Tuscany (Italy). We quantified litter mass and chemistry, root growth and turnover, CO 2 efflux from soils, and soil microbial biomass. Elevated CO 2 caused limited increases in aboveground production. Litter quality, fine root turnover, microbial biomass, root growth, and root biomass were not significantly affected by elevated CO 2 , except during some periods. Our results suggest that elevated atmospheric CO 2 might moderately accelerate inputs of organic matter to soil carbon pools in Mediterranean grasslands, but it may also partially accelerate losses of carbon from belowground by stimulating soil respiration.