title: Drought × CO2 interactions in trees: a test of the low-intercellular CO2 concentration (Ci ) mechanism.
abstract: Models of tree responses to climate typically project that elevated atmospheric CO2 concentration (eCa ) will reduce drought impacts on forests. We tested one of the mechanisms underlying this interaction, the 'low Ci effect', in which stomatal closure in drought conditions reduces the intercellular CO2 concentration (Ci ), resulting in a larger relative enhancement of photosynthesis with eCa , and, consequently, a larger relative biomass response. We grew two Eucalyptus species of contrasting drought tolerance at ambient and elevated Ca for 6-9 months in large pots maintained at 50% (drought) and 100% field capacity. Droughted plants did not have significantly lower Ci than well-watered plants, which we attributed to long-term changes in leaf area. Hence, there should not have been an interaction between eCa and water availability on biomass, and we did not detect one. The xeric species did have higher Ci than the mesic species, indicating lower water-use efficiency, but both species exhibited similar responses of photosynthesis and biomass to eCa , owing to compensatory differences in the photosynthetic response to Ci . Our results demonstrate that long-term acclimation to drought, and coordination among species traits may be important for predicting plant responses to eCa under low water availability.
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW, 2109, Australia.|School of Forest Science and Management, Department of Renewable Resources, University of Alberta, 4-29 Earth Sciences Building, Edmonton, AB, T6G 2E3, Canada.
authors.forename: Jeff W G
authors.initials: JW
authors.lastname: Kelly
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Remko A
authors.initials: RA
authors.lastname: Duursma
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW, 2109, Australia.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Atwell
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: David T
authors.initials: DT
authors.lastname: Tissue
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW, 2109, Australia.|Hawkesbury Institute for the Environment, Western Sydney University, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW, 2751, Australia.
authors.forename: Belinda E
authors.initials: BE
authors.lastname: Medlyn
mesh_terms: D018533:Biomass; D002245:Carbon Dioxide / Q000494:pharmacology*; D002980:Climate; D055864:Droughts; D005052:Eucalyptus / Q000187:drug effects / Q000502:physiology; D005110:Extracellular Space / Q000378:metabolism*; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology; D018526:Plant Transpiration / Q000187:drug effects / Q000502:physiology; D014197:Trees / Q000187:drug effects / Q000502:physiology*; D014867:Water
chemical_list: D014867:Water; D002245:Carbon Dioxide
keywords: Eucalyptus pilularis; Eucalyptus populnea; acclimation; drought; elevated atmospheric CO2 concentration; plant traits