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SOIL RESPIRED D13C SIGNATURES REFLECT ROOT EXUDATE OR ROOT TURNOVER SIGNATURES IN AN ELEVATED CO2 AND OZONE MESOCOSM EXPERIMENT
Citation:
Gregg, J W., C P. Andersen, AND P T. Rygiewicz. SOIL RESPIRED D13C SIGNATURES REFLECT ROOT EXUDATE OR ROOT TURNOVER SIGNATURES IN AN ELEVATED CO2 AND OZONE MESOCOSM EXPERIMENT. Presented at Application of Stable Isotope Techniques to Ecological Studies, Braunschweig, Germany, May 8-11, 2000.
Description:
Bulk tissue and root and soil respired d13C signatures were measured throughout the soil profile in a Ponderosa Pine mesocosm experiment exposed to ambient and elevated CO2 concentrations. For the ambient treatment, root (0-1mm, 1-2mm, and >2mm) and soil d13C signatures were ?24.9?.2? for both bulk and respired CO2 for six soil horizons (Oa, Oi, A, AC, C1 and C2) spanning 1m in depth. For the elevated CO2 treatments, soil signatures did not match the signatures of soil respired CO2. Rather, soil signatures remained constant at 24.9?.2? throughout the soil profile, whereas soil respired CO2 decreased with depth (?27.2?.2? for the Oa horizon through ?30.8?.2? in the C2 horizon). Since root respired CO2 signatures for the elevated CO2 treatment were quite negative (?39.7?.2?), we suggest that root exudates or root turnover had a large effect on soil respiration deeper in the profile where root biomass was greater in the mesocosms. CO2 from root decomposition and rapid metabolism of root exudates appeared to be respired first leaving more recalcitrant C pools in the soil horizons. In addition to introducing a new technique for measuring respired CO2 signatures, we also provide preliminary results of a survey comparison of tissue and respired CO2 signatures for a range of plant species.