Effects of elevated CO2 and N fertilization on soil respiration from ponderosa pine (Pine ponderosa) in open-top chambers
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 determine regulating mechanisms. Elevated CO 2 treatments were applied in open-top chambers containing 3-year-old ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings. Nitrogen 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 sulfate). Soils were irrigated to maintain soil moisture at >25%. Soil CO 2 evolution was measured over diurnal periods (20-22 h) in April, June, and October 1993 using a flow-through, infrared gas analyzer measurement system. To examine regulating mechanisms, we linked our results with other studies measuring root biomass with destructive sampling and root studies using minirhizotron techniques. Significantly higher soil CO 2 evolution was observed in the elevated CO 2 treatments in April and October; N effects were not significant. In October, integrated daily values for CO 2 evolution ranged from 3.73 to 15.68 g CO 2 m -2 day -1 for the ambient CO -2 + 0 N and 525 L L -1 CO 2 + 20 g m -2 N, respectively. Soil CO 2 flux among treatments was correlated with coarse root biomass (r 2 = 0.40; p >F = 0.0380), indicating that at least some of the variation observed among treatments was related to variation in root respiration. Across all sample periods and treatments, there was a significant correlation (r 2 = 0.63; p >F = 0.0001) between soil CO 2 evolution and percent fungal hyphae observed in minirhizotron tubes. Hence, some of the seasonal and treatment variation was also related to differences in heterotrophic activity.
Vose, James M.
Elliott, Katherine J.
Johnson, Dale W.
Walker, Roger F.
Johnson, Mark G.
Tingey, David T.
Can. J. For. Res. 25: 1243-1251 (1995)
Vose, James M.; Elliott, Katherine J.; Johnson, Dale W.; Walker, Roger F.; Johnson, Mark G.; Tingey, David T. 1995. Effects of elevated CO 2 and N fertilization on soil respiration from ponderosa pine (Pine ponderosa) in open-top chambers. Can. J. For. Res. 25: 1243-1251 (1995)