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Tree Physiology, 28:161–171
© 2008 Heron Publishing—Victoria, Canada
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Biophysical controls on rhizospheric and heterotrophic components of soil respiration in a boreal black spruce stand

David Gaumont-Guay (1, 2), T. Andrew Black (1), Alan G. Barr (3), Rachhpal S. Jassal (1) and Zoran Nesic (1)

1. Biometeorology and Soil Physics Group, University of British Columbia, Vancouver, BC V6T 1Z4, Canada / 2. Corresponding author () / 3. Climate Research Branch, Meteorological Service of Canada, Saskatoon, SK S7N 3H5, Canada / Received January 23, 2007; accepted June 12, 2007; published online December 3, 2007

Summary

We conducted a root-exclusion experiment in a 125-year-old boreal black spruce (Picea mariana (Mill.) BSP) stand in 2004 to quantify the physical and biological controls on temporal dynamics of the rhizospheric (R r) and heterotrophic (R h) components of soil respiration (R s). Annual R r, R h and estimated moss respiration were 285, 269 and 57 g C m–2 year–1, respectively, which accounted for 47, 44 and 9% of R s (611 g C m–2 year–1), respectively. A gradual transition from R h-dominated (winter, spring and fall) to R r-dominated (summer) respiration was observed during the year. Soil thawing in spring and the subsequent increase in soil water content (θ) induced a small and sustained increase in R h but had no effect on R r. During the remainder of the growing season, no effect of θ was observed on either component of R s. Both components increased exponentially with soil temperature (T s) during the growing season, but R r showed greater temperature sensitivity than R h (Q 10 of 4.0 and 3.0, respectively). Temperature-normalized variations in R r were highly correlated with eddy covariance estimates of gross ecosystem photosynthesis, and the correlation was greatest when R r was lagged by 24 days. Within diurnal cycles, variations in T s were highly coupled to variations in R h but were significantly decoupled from R r. The patterns observed at both time scales strongly suggest that the flow of photosynthates to the rhizosphere is a key driver of belowground respiration processes but that photosynthate supply may control these processes in several ways.

Keywords: heterotrophic respiration, photosynthesis, Picea mariana, rhizospheric respiration, soil CO2 efflux.

ISSN 0829-318X Copyright © 2002–2008 Heron Publishing Purchase this article: US$25.00