Short and Long‐Term Controls on Active Layer and Permafrost Carbon Turnover Across the Arctic.

Abstract: Decomposition of soil organic matter (SOM) in permafrost terrain and the production of greenhouse gases is a key factor for understanding climate change‐carbon feedbacks. Previous studies have shown that SOM decomposition is mostly controlled by soil temperature, soil moisture, and carbon‐nitrogen ratio (C:N). However, focus has generally been on site‐specific processes and little is known about variations in the controls on SOM decomposition across Arctic sites. For assessing SOM decomposition, we retrieved 241 samples from 101 soil profiles across three contrasting Arctic regions and incubated them in the laboratory under aerobic conditions. We assessed soil carbon losses (C_loss) five times during a 1 year incubation. The incubated material consisted of near‐surface active layer (AL_NS), subsurface active layer (AL_SS), peat, and permafrost samples. Samples were analyzed for carbon, nitrogen, water content, δ¹³C, δ¹⁵N, and dry bulk density (DBD). While no significant differences were observed between total AL_SS and permafrost C_loss over 1 year incubation (2.3 ± 2.4% and 2.5 ± 1.5% C_loss, respectively), AL_NS samples showed higher C_loss (7.9 ± 4.2%). DBD was the best explanatory parameter for active layer C_loss across sites. Additionally, results of permafrost samples show that C:N ratio can be used to characterize initial C_loss between sites. This data set on the influence of abiotic parameter on microbial SOM decomposition can improve model simulations of Arctic soil CO₂ production by providing representative mean values of CO₂ production rates and identifying standard parameters or proxies for upscaling potential CO₂ production from site to regional scales. [ABSTRACT FROM AUTHOR]