Abstract: Amethod was specially designed and applied for measuring CO₂ concentration of soil air over the non-waterlogged period of a rice-wheat rotation on an available area of about 1.6m² in a FACE (free-air CO₂ enrichment) study. Based on measuring the CO₂ concentration over the soil profile of 0～30 cm in depth using this method, the CO₂ profile in the soils of wheat fields under elevated and ambient CO₂ and the bare land under ambient CO₂ was investigated and some preliminary results were obtained. With in 0～30 cm in soil depth,CO₂ in the pores of the upper soil layers vertically diffused upwards much more quickly than that in the lower soil layers. During the period with active wheat growth, elevated atmospheric CO₂ by 200±40μmol·mol^-1 significantly increased the CO₂ concentration in soil air with in 0～30 cm in depth by 14%±5% (t-test, P<0.001).

Key words: driving factor, MOD17A3, NPP, vegetation, Shaanxi Pro-vince., spatio-temporal change