Abstract
Warming temperatures in continuous permafrost zones of the Arctic will alter both hydrological and geochemical soil conditions, which are strongly linked with heterotrophic microbial carbon (C) cycling. Heterogeneous permafrost landscapes are often dominated by polygonal features formed by expanding ice wedges: water accumulates in low centered polygons (LCPs), and water drains outward to surrounding troughs in high centered polygons (HCPs). These geospatial differences in hydrology cause gradients in biogeochemistry, soil C storage potential, and thermal properties. Presently, data quantifying carbon dioxide (CO2) and methane (CH4) release from HCP soils are needed to support modeling and evaluation of warming-induced CO2 and CH4 fluxes from tundra soils. This study quantifies the distribution of microbial CO2 and CH4 release in HCPs over a range of temperatures and draws comparisons to previous LCP studies. Arctic tundra soils were initially characterized for geochemical and hydraulic properties. Laboratory incubations at −2, +4, and +8°C were used to quantify temporal trends in CO2 and CH4 production from homogenized active layer organic and mineral soils in HCP centers and troughs, and methanogen abundance was estimated from mcrA gene measurements. Results showed that soil water availability, organic C, and redox conditions influence temporal dynamics and magnitude of gas production from HCP active layer soils during warming. At early incubation times (2–9 days), higher CO2 emissions were observed from HCP trough soils than from HCP center soils, but increased CO2 production occurred in center soils at later times (>20 days). HCP center soils did not support methanogenesis, but CH4-producing trough soils did indicate methanogen presence. Consistent with previous LCP studies, HCP organic soils showed increased CO2 and CH4 production with elevated water content, but HCP trough mineral soils produced more CH4 than LCP mineral soils. HCP mineral soils also released substantial CO2 but did not show a strong trend in CO2 and CH4 release with water content. Knowledge of temporal and spatial variability in microbial C mineralization rates of Arctic soils in response to warming are key to constraining uncertainties in predictive climate models.
Highlights
Arctic warming will transform tundra ecosystems by increasing soil temperatures and active layer depth, lengthening the annual active layer thaw period, and releasing large quantities of soil organic carbon (SOC) (Shaver et al, 1992; Schuur et al, 2009; Waldrop et al, 2010; Yergeau et al, 2010; Mackelprang et al, 2011; Lipson et al, 2013; Olefeldt et al, 2013)
X-ray diffraction (XRD) data from the high centered polygons (HCPs) center showed that all depths were dominated by quartz minerals with additional peaks representing albite, illite, and kaolinite (Supplementary Figure S4), expanding upon previous descriptions (Black, 1964)
No inorganic carbonate minerals were observed in the XRD patterns, indicating that carbonate mineral precipitation was absent in the HCP center soil
Summary
Arctic warming will transform tundra ecosystems by increasing soil temperatures and active layer depth, lengthening the annual active layer thaw period, and releasing large quantities of soil organic carbon (SOC) (Shaver et al, 1992; Schuur et al, 2009; Waldrop et al, 2010; Yergeau et al, 2010; Mackelprang et al, 2011; Lipson et al, 2013; Olefeldt et al, 2013). Controlled laboratory incubation studies are routinely used to identify the key drivers of gas emission patterns and the role of microbial properties like gene abundance, that in turn can inform model parameterization (Evans and Wallenstein, 2014; Faucherre et al, 2018; Philben et al, 2020a)
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