title: Informing climate models with rapid chamber measurements of forest carbon uptake.
abstract: Models predicting ecosystem carbon dioxide (CO2) exchange under future climate change rely on relatively few real-world tests of their assumptions and outputs. Here, we demonstrate a rapid and cost-effective method to estimate CO2exchange from intact vegetation patches under varying atmospheric CO2concentrations.We find that net ecosystem CO2uptake (NEE) in a boreal forest rose linearly by 4.7 ± 0.2% of the current ambient rate for every 10 ppm CO2increase, with no detectable influence of foliar biomass, season, or nitrogen (N) fertilization. The lack of any clear short-term NEE response to fertilization in such an N-limited system is inconsistent with the instantaneous downregulation of photosynthesis formalized in many global models. Incorporating an alternative mechanism with considerable empirical support - diversion of excess carbon to storage compounds - into an existing earth system model brings the model output into closer agreement with our field measurements. A global simulation incorporating this modified model reduces a long-standing mismatch between the modeled and observed seasonal amplitude of atmospheric CO2. Wider application of this chamber approach would provide critical data needed to further improve modeled projections of biosphere-atmosphere CO2exchange in a changing climate.
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, Lund, SE-223 62, Sweden.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Metcalfe
authors.affiliation: Environmental Sciences Division, Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6335, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Ricciuto
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, 27708-0328, USA.
authors.forename: Sari
authors.initials: S
authors.lastname: Palmroth
authors.affiliation: Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, SE-901 83, Sweden.
authors.forename: Catherine
authors.initials: C
authors.lastname: Campbell
authors.affiliation: Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, SE-901 83, Sweden.
authors.forename: Vaughan
authors.initials: V
authors.lastname: Hurry
authors.affiliation: Environmental Sciences Division, Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6335, USA.
authors.forename: Jiafu
authors.initials: J
authors.lastname: Mao
authors.affiliation: Institute for Sustainability Sciences, Agroscope, Zurich, 8046, Switzerland.
authors.forename: Sonja G
authors.initials: SG
authors.lastname: Keel
authors.affiliation: Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, Alnarp, SE-230 53, Sweden.
authors.forename: Sune
authors.initials: S
authors.lastname: Linder
authors.affiliation: Environmental Sciences Division, Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6335, USA.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Shi
authors.affiliation: Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, SE-901 83, Sweden.|Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, SE-901 83, Sweden.
authors.forename: Torgny
authors.initials: T
authors.lastname: Näsholm
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, SE-901 83, Sweden.
authors.forename: Klas E A
authors.initials: KE
authors.lastname: Ohlsson
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, SE-901 83, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Blackburn
authors.affiliation: Environmental Sciences Division, Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6335, USA.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Thornton
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, 27708-0328, USA.
authors.forename: Ram
authors.initials: R
authors.lastname: Oren
mesh_terms: D001272:Atmosphere; D002244:Carbon; D057486:Carbon Cycle; D002245:Carbon Dioxide; D002980:Climate; D057231:Climate Change; D017753:Ecosystem; D065928:Forests
chemical_list: D002245:Carbon Dioxide; D002244:Carbon
keywords: 
  Pinus sylvestris
  ; boreal forest; earth system model; model-data integration; nutrient limitation; photosynthetic downregulation