Soil respiration and microbial activity in a Mediterranean grassland exposed to Free Air CO2 Enrichment (FACE)

The effects of elevated atmospheric CO2 on in situ soil respiration and belowground biomass were Studied in a FACE (Free Air CO2 Enrichment) facility. A Mediterranean grassland community was exposed to elevated and ambient CO2 concentrations in a mini-FACE system in Tuscany (Italy). We quantified litter mass and chemistry, root growth and turnover, CO2 efflux from soils, and soil microbial biomass. Elevated CO2 caused limited increases in aboveground production. Litter quality, fine root turnover, microbial biomass, root growth, and root biomass were not significantly affected by elevated CO2, except during some periods. Our results suggest that elevated atmospheric CO2 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.