title: Decadal warming causes a consistent and persistent shift from heterotrophic to autotrophic respiration in contrasting permafrost ecosystems.
abstract: Soil carbon in permafrost ecosystems has the potential to become a major positive feedback to climate change if permafrost thaw increases heterotrophic decomposition. However, warming can also stimulate autotrophic production leading to increased ecosystem carbon storage-a negative climate change feedback. Few studies partitioning ecosystem respiration examine decadal warming effects or compare responses among ecosystems. Here, we first examined how 11 years of warming during different seasons affected autotrophic and heterotrophic respiration in a bryophyte-dominated peatland in Abisko, Sweden. We used natural abundance radiocarbon to partition ecosystem respiration into autotrophic respiration, associated with production, and heterotrophic decomposition. Summertime warming decreased the age of carbon respired by the ecosystem due to increased proportional contributions from autotrophic and young soil respiration and decreased proportional contributions from old soil. Summertime warming's large effect was due to not only warmer air temperatures during the growing season, but also to warmer deep soils year-round. Second, we compared ecosystem respiration responses between two contrasting ecosystems, the Abisko peatland and a tussock-dominated tundra in Healy, Alaska. Each ecosystem had two different timescales of warming (<5 years and over a decade). Despite the Abisko peatland having greater ecosystem respiration and larger contributions from heterotrophic respiration than the Healy tundra, both systems responded consistently to short- and long-term warming with increased respiration, increased autotrophic contributions to ecosystem respiration, and increased ratios of autotrophic to heterotrophic respiration. We did not detect an increase in old soil carbon losses with warming at either site. If increased autotrophic respiration is balanced by increased primary production, as is the case in the Healy tundra, warming will not cause these ecosystems to become growing season carbon sources. Warming instead causes a persistent shift from heterotrophic to more autotrophic control of the growing season carbon cycle in these carbon-rich permafrost ecosystems.
authors.affiliation: Earth Sciences Division, Climate Sciences Department, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720, USA.|Department of Biology, University of Florida, 220 Bartram Hall, Gainesville, FL, 32611, USA.
authors.forename: Caitlin E
authors.initials: CE
authors.lastname: Hicks Pries
authors.affiliation: Department of Systems Ecology, Institute of Ecological Science, VU University Amsterdam, De Boelelaan 1085, NL-1081 HV, Amsterdam, the Netherlands.
authors.forename: Richard S P
authors.initials: RS
authors.lastname: van Logtestijn
authors.affiliation: Department of Biology, University of Florida, 220 Bartram Hall, Gainesville, FL, 32611, USA.
authors.forename: Edward A G
authors.initials: EA
authors.lastname: Schuur
authors.affiliation: Department of Biology, University of Florida, 220 Bartram Hall, Gainesville, FL, 32611, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Natali
authors.affiliation: Department of Systems Ecology, Institute of Ecological Science, VU University Amsterdam, De Boelelaan 1085, NL-1081 HV, Amsterdam, the Netherlands.
authors.forename: Johannes H C
authors.initials: JH
authors.lastname: Cornelissen
authors.affiliation: Department of Systems Ecology, Institute of Ecological Science, VU University Amsterdam, De Boelelaan 1085, NL-1081 HV, Amsterdam, the Netherlands.
authors.forename: Rien
authors.initials: R
authors.lastname: Aerts
authors.affiliation: Climate Impacts Research Centre, Department of Ecology and Environmental Science, Umeå University, S-981 07, Abisko, Sweden.
authors.forename: Ellen
authors.initials: E
authors.lastname: Dorrepaal
mesh_terms: D000413:Alaska; D001110:Arctic Regions; D052818:Autotrophic Processes; D057486:Carbon Cycle; D057231:Climate Change; D057232:Global Warming; D052836:Heterotrophic Processes; D065946:Permafrost; D012621:Seasons; D012987:Soil / Q000737:chemistry*; D013548:Sweden; D065929:Tundra; D053833:Wetlands
chemical_list: D012987:Soil
keywords: autotrophic; carbon; climate change feedback; ecosystem respiration; heterotrophic; permafrost thaw; radiocarbon; warming experiment