title: Cumulative response of ecosystem carbon and nitrogen stocks to chronic CO₂ exposure in a subtropical oak woodland.
abstract: Rising atmospheric carbon dioxide (CO₂) could alter the carbon (C) and nitrogen (N) content of ecosystems, yet the magnitude of these effects are not well known. We examined C and N budgets of a subtropical woodland after 11 yr of exposure to elevated CO₂. We used open-top chambers to manipulate CO₂ during regrowth after fire, and measured C, N and tracer (15) N in ecosystem components throughout the experiment. Elevated CO₂ increased plant C and tended to increase plant N but did not significantly increase whole-system C or N. Elevated CO₂ increased soil microbial activity and labile soil C, but more slowly cycling soil C pools tended to decline. Recovery of a long-term (15) N tracer indicated that CO₂ exposure increased N losses and altered N distribution, with no effect on N inputs. Increased plant C accrual was accompanied by higher soil microbial activity and increased C losses from soil, yielding no statistically detectable effect of elevated CO₂ on net ecosystem C uptake. These findings challenge the treatment of terrestrial ecosystems responses to elevated CO₂ in current biogeochemical models, where the effect of elevated CO₂ on ecosystem C balance is described as enhanced photosynthesis and plant growth with decomposition as a first-order response.
authors.affiliation: Department of Biological Sciences and The Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, 86011, USA.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Hungate
authors.affiliation: Department of Biological Sciences and The Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, 86011, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Dijkstra
authors.affiliation: Department of Biological Sciences and The Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, 86011, USA.|US Geological Survey, Flagstaff, AZ, 86001, USA.
authors.forename: Zhuoting
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Department of Biological Sciences and The Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ, 86011, USA.|US Dairy Forage Research Center, USDA-ARS, Madison, WI, 53706, USA.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Duval
authors.affiliation: Department of Biological Sciences, Old Dominion University, Norfolk, VA, 23529, USA.
authors.forename: Frank P
authors.initials: FP
authors.lastname: Day
authors.affiliation: Department of Natural Resources and Environmental Science, University of Nevada, Reno, NV, 89557, USA.
authors.forename: Dale W
authors.initials: DW
authors.lastname: Johnson
authors.affiliation: Smithsonian Environmental Research Center, Edgewater, MD, 21037, USA.
authors.forename: J Patrick
authors.initials: JP
authors.lastname: Megonigal
authors.affiliation: Department of Biological Sciences, Old Dominion University, Norfolk, VA, 23529, USA.
authors.forename: Alisha L P
authors.initials: ALP
authors.lastname: Brown
authors.affiliation: Environmental Protection Agency, Microbiological and Chemical Exposure Assessment Research Division, Cincinnati, OH, 45268, USA.
authors.forename: Jay L
authors.initials: JL
authors.lastname: Garland
mesh_terms: D001272:Atmosphere; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D017753:Ecosystem; D004777:Environment; D005390:Fires; D009584:Nitrogen / Q000378:metabolism*; D058458:Nitrogen Cycle; D010788:Photosynthesis; D029963:Quercus / Q000254:growth & development / Q000378:metabolism*; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D014197:Trees; D014329:Tropical Climate
chemical_list: D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen
keywords: carbon cycling; elevated CO2; global change; long-term experiment; nitrogen cycling; scrub oak; soil carbon; subtropical woodland