HR: 10:50h
AN: B52A-03    [Abstracts]
TI: Partitioning Soil Respiration Between Autotrophic and Heterotrophic Components in a Mature Boreal Black Spruce Stand
AU: * Gaumont-Guay, D
EM: dgguay@interchange.ubc.ca
AF: Biometeorology and Soil Physics Group, University of British Columbia, 266B-2357 Main Mall , Vancouver, BC V6T 1Z4 Canada
AU: Black, T A
EM: andrew.black@ubc.ca
AF: Biometeorology and Soil Physics Group, University of British Columbia, 266B-2357 Main Mall , Vancouver, BC V6T 1Z4 Canada
AU: Barr, A G
EM: Alan.Barr@EC.GC.CA
AF: Climate Research Branch, Meteorological Service of Canada, 11 Innovation Blvd., Saskatoon, SK S7N 3H5 Canada
AU: Jassal, R S
EM: rachhpal@interchange.ubc.ca
AF: Biometeorology and Soil Physics Group, University of British Columbia, 266B-2357 Main Mall , Vancouver, BC V6T 1Z4 Canada
AU: Morgenstern, K
EM: kai.morgenstern@ubc.ca
AF: Biometeorology and Soil Physics Group, University of British Columbia, 266B-2357 Main Mall , Vancouver, BC V6T 1Z4 Canada
AU: Nesic, Z
EM: zoran.nesic@ubc.ca
AF: Biometeorology and Soil Physics Group, University of British Columbia, 266B-2357 Main Mall , Vancouver, BC V6T 1Z4 Canada
AB: A root-exclusion experiment conducted in mature boreal black spruce stand (125 year-old) in Saskatchewan, Canada, from September 2003 to December 2004 allowed the partitioning of soil respiration between autotrophic (roots, mycorrhizae and decomposers associated with the rhizosphere) and heterotrophic (free-living organisms) components using continuous automated chamber measurements of soil CO₂ efflux. The exclusion of live roots caused a 25% reduction in soil respiration three weeks after the application of the treatment in September 2003, which suggested a strong link between tree photosynthesis and belowground respiration processes. Annual estimates of autotrophic and heterotrophic respiration were 324 and 230 g C m^-2 y^-1 in 2004, accounting for 53 and 38% of soil respiration, respectively, after correcting for the decomposition of roots killed by trenching (78 g C m^-2 y^-1). The remainder (57 g C m^-2 y^-1) originated from live-moss respiration. Over the course of the year, there was a gradual transition from heterotrophic to autotrophic-dominated respiration with three distinctive phases: (1) autotrophic respiration was negligible during winter when the trees were dormant; (2) heterotrophic respiration dominated soil respiration during the shoulder periods of April-May and October-November when soil temperature was low; (3) autotrophic respiration exceeded heterotrophic respiration from mid-July to mid-September when soil temperature was high and trees were active. Both components of respiration increased exponentially with soil temperature during the growing season but autotrophic respiration showed greater temperature sensitivity than heterotrophic respiration. The replenishment of soil water following spring snowmelt induced a sustained increase in heterotrophic respiration. Pulses in autotrophic respiration were observed during summer following large rainfalls that were attributed to rhizosphere priming effects. After normalizing autotrophic respiration for the seasonal variation in soil temperature, it was found to be strongly correlated with tree photosynthesis. Analysis showed a lagged response with a maximum correlation for 15-25 days Tree photosynthesis also exerted a strong control on autotrophic respiration at the diurnal time scale with a lagged response of approximately 12 hours. These results suggest that the characterization of the soil temperature and water regimes is not sufficient to describe accurately the seasonal and diurnal variations in soil respiration and its components. Models need to incorporate the controls of aboveground photosynthetic production, photosynthate allocation and phloem transport on soil respiration.
DE: 1851 Plant ecology (0476)
DE: 1865 Soils (0486)
DE: 4806 Carbon cycling (0428)
DE: 4815 Ecosystems, structure, dynamics, and modeling (0439)
SC: Biogeosciences [B]
MN: Fall Meeting 2005