title: Changes in biomass allocation buffer low CO2effects on tree growth during the last glaciation.
abstract: Isotopic measurements on junipers growing in southern California during the last glacial, when the ambient atmospheric [CO2] (ca) was ~180 ppm, show the leaf-internal [CO2] (ci) was approaching the modern CO2compensation point for C3plants. Despite this, stem growth rates were similar to today. Using a coupled light-use efficiency and tree growth model, we show that it is possible to maintain a stable ci/caratio because both vapour pressure deficit and temperature were decreased under glacial conditions at La Brea, and these have compensating effects on the ci/caratio. Reduced photorespiration at lower temperatures would partly mitigate the effect of low cion gross primary production, but maintenance of present-day radial growth also requires a ~27% reduction in the ratio of fine root mass to leaf area. Such a shift was possible due to reduced drought stress under glacial conditions at La Brea. The necessity for changes in allocation in response to changes in [CO2] is consistent with increased below-ground allocation, and the apparent homoeostasis of radial growth, as caincreases today.
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia.|School of Archaeology, Geography and Environmental Sciences (SAGES), Reading University, Reading, UK.
authors.forename: Guangqi
authors.initials: G
authors.lastname: Li
authors.affiliation: Geography Department, Kansas State University, Manhattan, KS 66505, USA.
authors.forename: Laci M
authors.initials: LM
authors.lastname: Gerhart
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia.|School of Archaeology, Geography and Environmental Sciences (SAGES), Reading University, Reading, UK.
authors.forename: Sandy P
authors.initials: SP
authors.lastname: Harrison
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA.
authors.forename: Joy K
authors.initials: JK
authors.lastname: Ward
authors.affiliation: The La Brea Tar Pits Museum (George C. Page Museum), 5801 Wilshire Boulevard, Los Angeles, CA 90036, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Harris
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia.|AXA Chair of Biosphere and Climate Impacts, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5 7PY, UK.
authors.forename: I Colin
authors.initials: IC
authors.lastname: Prentice
mesh_terms: D018533:Biomass; D002140:California; D002245:Carbon Dioxide / Q000378:metabolism*; D002980:Climate; D008954:Models, Biological; D014197:Trees / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide