title: Circumpolar assessment of permafrost C quality and its vulnerability over time using long-term incubation data.
abstract: High-latitude ecosystems store approximately 1700 Pg of soil carbon (C), which is twice as much C as is currently contained in the atmosphere. Permafrost thaw and subsequent microbial decomposition of permafrost organic matter could add large amounts of C to the atmosphere, thereby influencing the global C cycle. The rates at which C is being released from the permafrost zone at different soil depths and across different physiographic regions are poorly understood but crucial in understanding future changes in permafrost C storage with climate change. We assessed the inherent decomposability of C from the permafrost zone by assembling a database of long-term (>1 year) aerobic soil incubations from 121 individual samples from 23 high-latitude ecosystems located across the northern circumpolar permafrost zone. Using a three-pool (i.e., fast, slow and passive) decomposition model, we estimated pool sizes for C fractions with different turnover times and their inherent decomposition rates using a reference temperature of 5 °C. Fast cycling C accounted for less than 5% of all C in both organic and mineral soils whereas the pool size of slow cycling C increased with C : N. Turnover time at 5 °C of fast cycling C typically was below 1 year, between 5 and 15 years for slow turning over C, and more than 500 years for passive C. We project that between 20 and 90% of the organic C could potentially be mineralized to CO2 within 50 incubation years at a constant temperature of 5 °C, with vulnerability to loss increasing in soils with higher C : N. These results demonstrate the variation in the vulnerability of C stored in permafrost soils based on inherent differences in organic matter decomposability, and point toward C : N as an index of decomposability that has the potential to be used to scale permafrost C loss across landscapes.
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL, USA.
authors.forename: Christina
authors.initials: C
authors.lastname: Schädel
authors.forename: Edward A G
authors.initials: EA
authors.lastname: Schuur
authors.forename: Rosvel
authors.initials: R
authors.lastname: Bracho
authors.forename: Bo
authors.initials: B
authors.lastname: Elberling
authors.forename: Christian
authors.initials: C
authors.lastname: Knoblauch
authors.forename: Hanna
authors.initials: H
authors.lastname: Lee
authors.forename: Yiqi
authors.initials: Y
authors.lastname: Luo
authors.forename: Gaius R
authors.initials: GR
authors.lastname: Shaver
authors.forename: Merritt R
authors.initials: MR
authors.lastname: Turetsky
mesh_terms: D001110:Arctic Regions; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D057231:Climate Change; D017753:Ecosystem; D008954:Models, Biological; D012621:Seasons; D012987:Soil / Q000737:chemistry*; D013696:Temperature
chemical_list: D012987:Soil; D002244:Carbon
keywords: Alaska; C decomposition; Siberia; boreal forest; climate change; soil organic carbon; tundra