title: Nonlinear CO2flux response to 7 years of experimentally induced permafrost thaw.
abstract: Rapid Arctic warming is expected to increase global greenhouse gas concentrations as permafrost thaw exposes immense stores of frozen carbon (C) to microbial decomposition. Permafrost thaw also stimulates plant growth, which could offset C loss. Using data from 7 years of experimental Air and Soil warming in moist acidic tundra, we show that Soil warming had a much stronger effect on CO2flux than Air warming. Soil warming caused rapid permafrost thaw and increased ecosystem respiration (Reco), gross primary productivity (GPP), and net summer CO2storage (NEE). Over 7 years Reco, GPP, and NEE also increased in Control (i.e., ambient plots), but this change could be explained by slow thaw in Control areas. In the initial stages of thaw, Reco, GPP, and NEE increased linearly with thaw across all treatments, despite different rates of thaw. As thaw in Soil warming continued to increase linearly, ground surface subsidence created saturated microsites and suppressed Reco, GPP, and NEE. However Recoand GPP remained high in areas with large Eriophorum vaginatum biomass. In general NEE increased with thaw, but was more strongly correlated with plant biomass than thaw, indicating that higher Recoin deeply thawed areas during summer months was balanced by GPP. Summer CO2flux across treatments fit a single quadratic relationship that captured the functional response of CO2flux to thaw, water table depth, and plant biomass. These results demonstrate the importance of indirect thaw effects on CO2flux: plant growth and water table dynamics. Nonsummer Recomodels estimated that the area was an annual CO2source during all years of observation. Nonsummer CO2loss in warmer, more deeply thawed soils exceeded the increases in summer GPP, and thawed tundra was a net annual CO2source.
authors.affiliation: Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA.
authors.forename: Marguerite
authors.identifier: 0000-0001-8733-9119
authors.initials: M
authors.lastname: Mauritz
authors.affiliation: School of Forest Resources and Conservation, University of Florida, Gainesville, FL, USA.
authors.forename: Rosvel
authors.initials: R
authors.lastname: Bracho
authors.affiliation: Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Celis
authors.affiliation: Department of Geological Sciences, University of Florida, Gainesville, FL, USA.
authors.forename: Jack
authors.initials: J
authors.lastname: Hutchings
authors.affiliation: Woods Hole Research Center, Falmouth, MA, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Natali
authors.affiliation: Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA.
authors.forename: Elaine
authors.initials: E
authors.lastname: Pegoraro
authors.affiliation: Environmental Sciences Division and Climate Change Sciences Institute, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
authors.forename: Verity G
authors.initials: VG
authors.lastname: Salmon
authors.affiliation: Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA.
authors.forename: Christina
authors.initials: C
authors.lastname: Schädel
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL, USA.
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Webb
authors.affiliation: Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, USA.
authors.forename: Edward A G
authors.initials: EAG
authors.lastname: Schuur
mesh_terms: D001110:Arctic Regions; D057486:Carbon Cycle; D002245:Carbon Dioxide; D065946:Permafrost; D012987:Soil; D065929:Tundra
chemical_list: D012987:Soil; D002245:Carbon Dioxide
keywords: Arctic; carbon; ecosystem respiration; experimental warming; gross primary productivity; net ecosystem exchange; permafrost; thaw; tundra