B11C-0434
Allocation changes buffer CO2 effect on tree growth since the last ice age
Monday, 14 December 2015
Poster Hall (Moscone South)
Guangqi Li1, Sandy P Harrison2, Iain C Prentice3, Laci M Gerhart4 and Joy K. Ward4, (1)University of Reading, GEography and Environmental Sciences, Reading, RG6, United Kingdom, (2)University of Reading, Reading, United Kingdom, (3)AXA Chair of Biosphere and Climate Impacts, Grand Challenges in Ecosystems and the Environment and Grantham Institute, Climate Change and the Environment, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5, London, United Kingdom, (4)University of Kansas, Lawrence, KS, United States
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 close to the modern CO2 compensation point for C3 plants. Despite this, stem growth rates were similar to today. Using a coupled light-use efficiency and tree growth model, we show that the ci/ca ratio was stable because both vapor pressure deficit and temperature were decreased with compensating effects. Reduced photorespiration at lower temperatures partly mitigated the effect of low ci on gross primary production, but maintenance of present-day radial growth also required changes in carbon allocation, including a ~25% reduction in below-ground carbon allocation and a ~7% in allocation to leaves. Such a shift was possible due to reduced drought stress. Our findings are consistent with the observed increase in below-ground allocation in FACE experiments and the apparent homoeostasis of measured radial growth as ca increases today; results which our model can also reproduce.
