title: Short-term carbon cycling responses of a mature eucalypt woodland to gradual stepwise enrichment of atmospheric CO2 concentration.
abstract: Projections of future climate are highly sensitive to uncertainties regarding carbon (C) uptake and storage by terrestrial ecosystems. The Eucalyptus Free-Air CO2 Enrichment (EucFACE) experiment was established to study the effects of elevated atmospheric CO2 concentrations (eCO2 ) on a native mature eucalypt woodland with low fertility soils in southeast Australia. In contrast to other FACE experiments, the concentration of CO2 at EucFACE was increased gradually in steps above ambient (+0, 30, 60, 90, 120, and 150 ppm CO2 above ambient of ~400 ppm), with each step lasting approximately 5 weeks. This provided a unique opportunity to study the short-term (weeks to months) response of C cycle flux components to eCO2 across a range of CO2 concentrations in an intact ecosystem. Soil CO2 efflux (i.e., soil respiration or Rsoil ) increased in response to initial enrichment (e.g., +30 and +60 ppm CO2 ) but did not continue to increase as the CO2 enrichment was stepped up to higher concentrations. Light-saturated photosynthesis of canopy leaves (Asat ) also showed similar stimulation by elevated CO2 at +60 ppm as at +150 ppm CO2 . The lack of significant effects of eCO2 on soil moisture, microbial biomass, or activity suggests that the increase in Rsoil likely reflected increased root and rhizosphere respiration rather than increased microbial decomposition of soil organic matter. This rapid increase in Rsoil suggests that under eCO2, additional photosynthate was produced, transported belowground, and respired. The consequences of this increased belowground activity and whether it is sustained through time in mature ecosystems under eCO2 are a priority for future research.
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: John E
authors.initials: JE
authors.lastname: Drake
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Catriona A
authors.initials: CA
authors.lastname: Macdonald
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Tjoelker
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Kristine Y
authors.initials: KY
authors.lastname: Crous
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.|INRA UMR 1391, ISPA, CS 20032, F-33140, Villenave d'Ornon, France.
authors.forename: Teresa E
authors.initials: TE
authors.lastname: Gimeno
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Brajesh K
authors.initials: BK
authors.lastname: Singh
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.|Department of Forest Resources, University of Minnesota, 1530 Cleveland Avenue North, St. Paul, MN 55108, USA.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Reich
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Ian C
authors.initials: IC
authors.lastname: Anderson
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: David S
authors.initials: DS
authors.lastname: Ellsworth
mesh_terms: D001272:Atmosphere / Q000737:chemistry; D001315:Australia; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D057231:Climate Change; D017753:Ecosystem; D005052:Eucalyptus / Q000378:metabolism; D065928:Forests; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism; D012987:Soil / Q000737:chemistry
chemical_list: D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon
keywords: Eucalyptus; carbon cycling; climate change; elevated carbon dioxide; woodland