Resilience of Arctic Permafrost Carbon in Mackenzie River Basin: An Incubation Experiment to Observe Priming Potentials and Biodegradability of Arctic Permafrost Peatlands

Abstract:

Arctic permafrost zones cover 25% of the Northern Hemisphere and hold 1672Pg of soil carbon (C) with 277Pg in Arctic permafrost peatlands, which is 1/3 of the CO₂ in the atmosphere. This currently protected C is a potential source for increased emissions in a warmer climate. Longer growing seasons resulting in increased plant productivity above and below ground may create new labile C inputs with the potential to affect mineralization of previously stable SOM, known as the priming effect. This study examined the response of soil respiration to labile substrate addition in carbon-rich (42-48 %C) permafrost peatland soils along a N-S transect in the central Mackenzie River Basin (69.2-62.6°N). Active layer and near surface soils (surface Δ14C values > -140.0) were collected from four sites between -10.5 and -5.2 MAT. Soils were spiked with 0.5 mg D-glucose g^-1soil, and incubated at 10°C for 23 days to determine potential, short term (i.e., apparent) priming effects.

On average glucose addition increased respiration in all samples. One site showed priming evidence in active layer soils despite one-way ANOVA not illustrating statistically significant differences between control and treated final cumulative CO₂. Apparent priming effects were seen in two near surface permafrost samples, however cumulative increases in CO₂ were not identified as significant. When all results from all sites and depths were considered, the addition of glucose showed no significant effect on total CO2 production relative to controls (p=0.957), suggesting that these sites may be resilient to increased inputs in that little priming evidence was observed. To test the idea that the soils that showed priming effects are of poorer quality, we conducted an additional incubation experiment to explore the biodegradability of these permafrost peatland soils. Soils from these four sites were inoculated and incubated for 17 days. The two sites with observed priming showed the highest biodegradability; suggesting that, compared to other soils, permafrost peat soils may not be sensitive to the priming effect and respond uniquely to warming and increased litter inputs. Therefore C loss from priming decomposition may be trivial when compared to other C loss mechanisms in Arctic permafrost peatlands.