Soil respiration response to three years of elevated CO2 and N fertilization in ponderosa pine (Pinus ponderosa Doug. ex Laws.)
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 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 > 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 (10cm soil depth) and decreased dramatically at temperatures > 18 C. These patterns indicate exceeding optimal temperatures for biological activity. The dynamic, how-through measurement system was weakly correlated (r = 0.57; p 2 measurement method.
Vose, James M.
Elliott, Katherine J.
Johnson, Dale W.
Tingey, David T.
Johnson, Mark G.
Plant and Soil 190: 19-28, 1997.
Vose, James M.; Elliott, Katherine J.; Johnson, Dale W.; Tingey, David T.; Johnson, Mark G. 1997. 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: 19-28, 1997.