Temperature Sensitivity of Northern Soils Using Flux-concentration Measurements and Inversion Analysis

Northern soils are vast reservoirs of carbon and even small changes in soil CO2 respiration could significantly alter atmospheric concentrations. Recent synthetic modeling studies have shown that the temperature sensitivity (Q10) of soil respiration is most accurately solved using a combination of subsurface and surface flux measurements. This new approach should be possible even in short-term studies where traditional approaches are confused by diel hysteretic behavior in soil respiration. Here we present the results of a study at five field sites on a latitudinal gradient in Alaska during the 2016 growing season. We used low-power automated multiplexer soil gas systems at each site that measured soil surface CO2 flux from 3 surface forced diffusion chambers, and soil profile concentrations from 3 soil depth chambers every 30 min. HOBO Onset dataloggers were used to monitor soil moisture and temperature profiles. We hypothesized that moisture gradients across these sites, and within the soils, would be a determinant of Q10. We applied both traditional, and inversion approaches, for solving temperature sensitivity, as applied to increasingly short-term datasets. We were able to confirm that using soil subsurface CO2 alongside surface CO2 flux within the inversion provided the most reasonable estimates of Q10 on short timeseries - which is very useful for northern work given short field seasons and limited field accessibility. Soil moisture content had an important influence on temperature sensitivity across the different field sites. This study shows that coupled approaches to sampling and analysis can contribute to a faster understanding of permafrost soil carbon.