USING STABLE ISOTOPES TO DETERMINE SOIL CARBON INPUT DIFFERENCES UNDER AMBIENT AND ELEVATED ATMOSPHERIC CO2 CONDITIONS

Quantitative estimates of soil C input under ambient (35 Pa) and eleva ted (60 Pa) CO2-partial pressure (pCO(2)) were determined in a Free-Ai r Carbon dioxide Enrichment (FACE) experiment. To facilitate C-13-trac ing, Trifolium repens L. was grown in a soil with an initial delta(13) C distinct by at least 5 parts per thousand from the delta(13)C of T. repens grown under ambient or elevated pCO(2). A shift in delta(13)C O f the soil organic C was detected after one growing season. Calculated new soil C inputs in soil under ambient and elevated pCO(2) were 2 an d 3 t ha(-1), respectively. Our findings suggest that under elevated C O2 conditions, soil C sequestration may be altered by changes in plant biomass production and quality.