Abstract
Abstract. Soil respiration is a key ecosystem function whereby shifts in respiration rates can shift systems from carbon sinks to sources. Soil respiration in permafrost-associated systems is particularly important given climate change driven permafrost thaw that leads to significant uncertainty in resulting ecosystem carbon dynamics. Here we characterize the spatial structure and environmental drivers of soil respiration across a permafrost transition zone. We find that soil respiration is characterized by a non-linear threshold that occurs at active-layer depths greater than 140 cm. We also find that within each season, tree basal area is a dominant driver of soil respiration regardless of spatial scale, but only in spatial domains with significant spatial variability in basal area. Our analyses further show that spatial variation (the coefficient of variation) and mean-variance power-law scaling of soil respiration in our boreal system are consistent with previous work in other ecosystems (e.g., tropical forests) and in population ecology, respectively. Comparing our results to those in other ecosystems suggests that temporally stable features such as tree-stand structure are often primary drivers of spatial variation in soil respiration. If so, this provides an opportunity to better estimate the magnitude and spatial variation in soil respiration through remote sensing. Combining such an approach with broader knowledge of thresholding behavior – here related to active layer depth – would provide empirical constraints on models aimed at predicting ecosystem responses to ongoing permafrost thaw.
Highlights
Given its central role in global carbon cycling (Raich and Potter, 1995), the flux of CO2 from soil to the atmosphere – collectively referred to as soil respiration (SR) – is heavily studied across a broad range of systems and spatiotemporal scales using methods ranging from small footprint flux chambers to large footprint flux towers (Bond-Lamberty and Thomson, 2010; Wolf et al, 2016)
SR measured in a soil collar in Summer was strongly correlated to SR measured in the same soil collar in the Fall (Fig. S1)
active layer depth (ALD) at the western boundary of the sampled domain showed threshold behavior, increasing rapidly at spatial positions near ∼ 30–35 m and reached its limit (150 cm) at about 50 m (Fig. 4a and b). These patterns in SR variation and ALD were found in both seasons even though www.biogeosciences.net/14/4341/2017/
Summary
Given its central role in global carbon cycling (Raich and Potter, 1995), the flux of CO2 from soil to the atmosphere – collectively referred to as soil respiration (SR) – is heavily studied across a broad range of systems and spatiotemporal scales using methods ranging from small footprint flux chambers to large footprint flux towers (Bond-Lamberty and Thomson, 2010; Wolf et al, 2016). Our understanding of SR patterns is inherently linked to the scales at which measurements are made and we often lack knowledge of how the variation in SR changes as we move across scales. To rigorously and mechanistically link SR measurements across scales, it is essential to understand spatial heterogeneity in SR, how spatial heterogeneity changes across scales, and the environmental features that drive those SR patterns. Knowledge of SR spatial heterogeneity – and underlying drivers of that heterogeneity – in permafrost associated ecosystems is important given the large carbon stocks in permafrost (Tarnocai et al, 2009) and ongoing permafrost thaw (Grosse et al, 2011; Schuur et al, 2013, 2015). Numerous studies have investigated temporal dynamics of SR and most find strong influences of temperature and moisture (e.g., Davidson et al, 1998; Hanson et al, 1993), but much less is known about spatial variation in SR, where temperature and moisture appear to have weaker influences (Yim et al, 2003; Dore et al, 2014; Ohashi et al, 2015; Song et al, 2013).
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