A comparison of trenched plot techniques for partitioning soil respiration

Partitioning the soil surface CO2 flux (R-S) flux is an important step in understanding ecosystem-level carbon cycling, given that R-S is poorly constrained and its source components may have different sensitivities to climate change. Trenched plots are an inexpensive but labor-intensive method of separating the R-S flux into its root (autotrophic) and soil (heterotrophic) components. This study tested if various methods of plant suppression in trenched plots affected R-S fluxes, quantified the R-S response to soil temperature and moisture changes, and estimated the heterotrophic contribution to R-S. It was performed in a boreal black spruce (Picea mariana) plantation, using a randomized complete block design, during the 2007 and 2008 growing seasons. Trenched plots had significantly lower R-S than control plots, with differences appearing similar to 100 days after trenching; spatial variability doubled immediately after trenching but then declined throughout the experiment. Most trenching treatments had significantly lower (by similar to 0.5 umol CO2 m(-2) s(-1)) R-S than the controls, and there was no significant difference in R-S among the various trenching treatments. Soil temperature at 2 cm explained more R-S variability than did 10-cm temperature or soil moisture. Temperature sensitivity (Q(10)) declined in the control plots from similar to 2.6 (at 5 degrees C) to similar to 1.6 (at 15 degrees C): trenched plots values were higher, from 3.1 at 5 degrees C to 1.9 at 15 degrees C. We estimated R-S for the study period to be 241 +/- 40 g C m(-2), with live roots contributing 64% of Rs after accounting for fine root decay, and 293 g C m(-2) for the entire year. These findings suggest that laborious hand weeding of trenched plot vegetation may be replaced by other methods, facilitating future studies of this large and poorly-understood carbon flux. Published by Elsevier Ltd.