A comparison of trenched plot techniques for partitioning soil respiration

Abstract

Partitioning the soil surface CO 2 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 ∼100 days after trenching; spatial variability doubled immediately after trenching but then declined throughout the experiment. Most trenching treatments had significantly lower (by ∼0.5 μmol CO 2 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 ∼2.6 (at 5 °C) to ∼1.6 (at 15 °C); trenched plots values were higher, from 3.1 at 5 °C to 1.9 at 15 °C. We estimated R S for the study period to be 241 ± 40 g C m −2, with live roots contributing 64% of R S 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.