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Soil respiration response to three years of elevated CO₂ and N fertilization in ponderosa pine (Pinus ponderosa Doug. ex Laws.)

James M. Vose, Katherine J. Elliott, Dale W. Johnson, David T. Tingey and Mark G. Johnson
Plant and Soil
Vol. 190, No. 1 (March (I) 1997), pp. 19-28
Published by: Springer
Stable URL: http://www.jstor.org/stable/42947987
Page Count: 10
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Soil respiration response to three years of elevated CO₂ and N fertilization in ponderosa pine (Pinus ponderosa Doug. ex Laws.)
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Abstract

We measured growing season soil CO₂ evolution under elevated atmospheric [CO₂] and soil nitrogen (N) additions. Our objectives were to determine treatment effects, quantify seasonal variation, and compare two measurement techniques. Elevated [CO₂] 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 CO₂ (ambient, + 175, and + 350 μL L⁻¹ CO₂) and N (0, 10, and 20 g m⁻² N as ammonium sulphate). Soils were irrigated to maintain soil moisture at > 25 percent. Soil CO₂ 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 pCO₂ measurements were made with gas wells. Significantly higher soil CO₂ evolution was observed in the elevated CO₂ treatments; N effects were not significant. Averaged across all measurement periods, fluxes, were 4.8, 8.0, and 6.5 for ambient + 175 CO₂, and + 350 CO₂ respectively). Treatment variation was linearly related to fungal occurrence as observed in minirhizotron tubes. Seasonal variation in soil CO₂ evolution was non-linearly related to soil temperature; i.e., fluxes increased up to approximately soil temperature (10cm soil depth) and decreased dramatically at temperatures > 18 °C. These patterns indicate exceeding optimal temperatures for biological activity. The dynamic, flow-through measurement system was weakly correlated (r = 0.57; p < 0.0001; n = 56) with the pCO₂ measurement method.

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