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SOIL RESPIRATION RESPONSE TO THREE YEARS OF ELEVATED CO-2 AND N FERTILIZATION IN PONDEROSA PINE (PINUS PONDEROSA DOUG. EX LAWS.)
Vose, J. M., K. J. Elliott, D. W. Johnson, D. Tingey, AND M. Johnson. SOIL RESPIRATION RESPONSE TO THREE YEARS OF ELEVATED CO-2 AND N FERTILIZATION IN PONDEROSA PINE (PINUS PONDEROSA DOUG. EX LAWS.). Plant and Soil 190(1):19-28, (1997).
We measured growing season soil CO-2 evolution under elevated atmospheric (CO-2) and soil nitrogen (N) additions. Our objectives were to determine treatment effects, quantify seasonal variation, and compare two measurement techniques. Elevated (CO-2) treatments were applied in open-top chambers containing ponderosa pine (Pinus ponderosa L.) seedlings. N applications were made annually in early spring. The experimental design was a replicated factorial combination of CO-2 (ambient, + 175, and +350 mu-L L-1 CO-2) and N(0,10, and 20 g m-2 N as ammonium sulphate). Soils were irrigated to maintain soil moisture at gt 25 percent. Soil CO-2 evolution was measured over diurnal periods (20-22 hours) in October 1992, and April, June, and October 1993 and 1994 using a flow-through, infrared gas analyzer measurement system and corresponding PCO-2 measurements were made with gas wells. Significantly higher soil CO-2 evolution was observed in the elevated CO-2 treatments; N effects were not significant. Averaged across all measurement periods, fluxes, were 4.8, 8.0, and 6.5 for ambient + 175 CO-2, and +350 CO-2 respectively). Treatment variation was linearly related to fungal occurrence as observed in minirhizotron tubes. Seasonal variation in soil CO-2 evolution was non-linearly related to soil temperature; i.e., fluxes increased up to approximately soil temperature (10 cm soil depth) and decreased dramatically at temperatures gt 18 degree C. These patterns indicate exceeding optimal temperatures for biological activity. The dynamic, flow-through measurement system was weakly correlated (r=0.57;p lt 0.0001; n=56) with the pCO-2 measurement method.
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Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT