Document: CRE-3-59-89

Soil respiration and total belowground carbon allocation in developing Pinus contorta forests, Yellowstone National Park.

LITTON, C.M.* ¹, M.G.RYAN ², D.B.TINKER ¹ and D.H.KNIGHT ¹

University of Wyoming, Laramie, WY 82071-3165 ¹
USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO 80526-2098 ²

Abstract:
Soil respiration, or CO₂ efflux, is considered to be the sum of all belowground metabolic functions in which CO₂ is produced, and includes plant root respiration, microbial respiration and faunal respiration. It has been used for comparisons of ecosystem function and is one of the principal variables required for the calculation of Total Belowground Carbon Allocation (TBCA). In the summer of 1999, soil respiration measurements were taken five times on 60 points in three developing stands representing different stand structures (low, medium, and high sapling density with herbaceous plant cover values that decrease with increasing sapling density). CO₂ efflux was determined with an Infrared Gas Analyzer (IRGA). Each IRGA measurement was coupled with a measurement of soil temperature at 10 cm. Soil temperature alone was found to be a very poor indicator of soil respiration for the entire season (r² = 0.007), but a relatively good predictor for 24-hr periods. To examine the effect of soil moisture on soil respiration, we compared CO₂ efflux under dry and wet conditions at similar soil temperatures (2C). A paired t-test revealed significant differences in soil respiration rates between "dry" and "wet" conditions (P < 0.0001), illustrating the importance of soil moisture on soil respiration rates. Biweekly CO₂ efflux measurements analyzed with a repeated measures GLM differed with stand structure (P < 0.01). Mean flux for the high sapling density plot was 0.24 g CO₂ m^-2 hr^-1, compared with 0.17 g CO₂ m^-2 hr^-1 for the low density site. Carbon dioxide efflux declined during the summer as soils dried (P < 0.01), from a mean of 0.27 g CO₂ m^-2 hr^-1 on June 28 to 0.09 g CO₂ m^-2 hr^-1 on October 9. In general, CO₂ efflux was highest on the high sapling density site, intermediate on the moderate density site, and lowest on the low density site. Assuming that changes in litter and soil carbon pools are minimal, soil respiration constitutes the majority of TBCA, and contrasts in TBCA represent important differences in belowground carbon allocation in stands differing in structure.

Keywords: soil respiration, CO₂ efflux, total belowground carbon allocation

This abstract is being presented at: 10:30 AM in session:
Poster Session #13: Decomposition and Soil Respiration.