Total forest soil respiration is a large component of ecosystem respiration. We need a detailed understanding of controls over soil respiration rates in order to anticipate the effect of future climate change on forest carbon balance. A significant hole in our understanding of respiration controls is in the relative importance of abiotic controls such as soil temperature vs biologically-driven substrate controls. Previous work at a forested site in northern Idaho suggests that soil respiration is suppressed by the late-summer drought, but it is not known whether this is due to a lack of moisture or of high-quality substrate. In 2008, we studied the combined influence of soil temperature, soil moisture, and substrate availability by experimental additions of substrate and moisture. After treatment, we monitored soil respiration using an automated system (ACES). The additions were applied from June through October 2008.

Results/Conclusions Results show a similar response of soil respiration to both sugar additions and water additions throughout the growing season. Soil respiration was only slightly elevated in response to water additions. Although ambient respiration rates were suppressed in late summer, we saw no apparent change in moisture limitation, perhaps because the surface soils never dried below -0.5 MPa. The depression may have been due to a decrease in root respiration, indicating dominance of root respiration over microbial respiration at this site in this year.