Elevated CO2 stimulates soil respiration in a FACE wheat field

Understanding the response of soil carbon (C) dynamics to higher atmospheri c CO2 concentrations is critical for evaluating the potential for soil C se questration on time scales of decades to centuries. Here, we report on chan ges in soil respiration under Free-Air CO2 Enrichment (FACE) where spring w heat was grown in an open field at two CO2 concentrations (ambient and ambi ent+200 pmol mol(-1)), under natural meteorological conditions. FACE increa sed soil respiration rates by 40-70% during the peak of wheat growth. On th e FACE plots, stable C isotopic composition Of soil CO2 was used to partiti on the soil CO2 flux into C from rhizosphere respiration and decomposition of pre-existing C. Decomposition contributed 100% of the soil CO2 flux befo re crop growth commenced, and only 35-45% of the flux at the peak of the gr owing season. Decomposition rates were not correlated with soil temperature , but rhizosphere respiration rates were strongly correlated with green lea f area index.