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A STABLE ISOTOPE ANALYSIS OF SOIL CARBON DENSITY FRACTIONS FOLLOWING 4 YEARS OF CONTINUOUS CLIMATE CHANGE EXPOSURE IN A DOUGLAS FIR MESOCOSM STUDY
Citation:
Johnson, M G. AND P T. Rygiewicz. A STABLE ISOTOPE ANALYSIS OF SOIL CARBON DENSITY FRACTIONS FOLLOWING 4 YEARS OF CONTINUOUS CLIMATE CHANGE EXPOSURE IN A DOUGLAS FIR MESOCOSM STUDY. Presented at Soil Science Socity of America annual meeting, Denver, CO, November 2-6, 2003.
Description:
We conducted a 4-year full-factorial study of the effects of elevated atmospheric CO2 and temperature on Douglas fir seedlings growing in reconstructed native forest soils in mesocosms. The elevated CO2 treatment was ambient CO2 plus 200 ppm CO2. The elevated temperature treatment was ambient temperature plus 4 degrees C. The CO2 source was depleted in 13C and provided a stable isotope tracer of newly fixed C. At the end of the study soil samples were collected by horizon and density fractionated. Density fractionation provides a means of separating kinetic C fractions with the denser fractions representing older more recalcitrant C. Soil C concentration and del 13C were measured. C concentration decreased both with depth in the soil and as the fraction density increased. There was a -3 per mil difference between the heavy and light density fractions. Elevated CO2 led to an increase in depleted 13C in the uppermost horizons and in the lightest density fractions, while elevated temperature decreased soil C concentrations in the upper horizons. Elevated CO2 appears to affect the chemistry of the lightest density fractions, which are more like plant material and the least decomposed compared with C in the heavier density fractions.