title: Dynamics of soil CO2efflux under varying atmospheric CO2concentrations reveal dominance of slow processes.
abstract: We evaluated the effect on soil CO2efflux (FCO2) of sudden changes in photosynthetic rates by altering CO2concentration in plots subjected to +200 ppmv for 15 years. Five-day intervals of exposure to elevated CO2(eCO2) ranging 1.0-1.8 times ambient did not affect FCO2. FCO2did not decrease until 4 months after termination of the long-term eCO2treatment, longer than the 10 days observed for decrease of FCO2after experimental blocking of C flow to belowground, but shorter than the ~13 months it took for increase of FCO2following the initiation of eCO2. The reduction of FCO2upon termination of enrichment (~35%) cannot be explained by the reduction of leaf area (~15%) and associated carbohydrate production and allocation, suggesting a disproportionate contraction of the belowground ecosystem components; this was consistent with the reductions in base respiration and FCO2-temperature sensitivity. These asymmetric responses pose a tractable challenge to process-based models attempting to isolate the effect of individual processes on FCO2.
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, USA.|Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA.
authors.forename: Dohyoung
authors.identifier: 0000-0002-6499-8370
authors.initials: D
authors.lastname: Kim
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, USA.
authors.forename: Ram
authors.initials: R
authors.lastname: Oren
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Clark
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, USA.
authors.forename: Sari
authors.initials: S
authors.lastname: Palmroth
authors.affiliation: USDA Forest Service, Southern Research Station, Coweeta Hydrologic Laboratory, Otto, NC, USA.
authors.forename: A Christopher
authors.initials: AC
authors.lastname: Oishi
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, USA.
authors.forename: Heather R
authors.initials: HR
authors.lastname: McCarthy
authors.affiliation: USDA Forest Service, Southern Research Station, Research Triangle Park, NC, USA.
authors.forename: Chris A
authors.initials: CA
authors.lastname: Maier
authors.affiliation: USDA Forest Service, Southern Research Station, Asheville, NC, USA.
authors.forename: Kurt
authors.initials: K
authors.lastname: Johnsen
mesh_terms: D002245:Carbon Dioxide; D017753:Ecosystem; D010788:Photosynthesis; D018515:Plant Leaves; D012987:Soil / Q000737:chemistry*
chemical_list: D012987:Soil; D002245:Carbon Dioxide
keywords: Bayesian state space model; carbon dioxide; climate change; nitrogen fertilization; soil respiration