Mechanisms linking plant productivity and water status for a temperate Eucalyptus forest flux site: analysis over wet and dry years with a simple model
David A. Pepper A E , Ross E. McMurtrie A , Belinda E. Medlyn B , Heather Keith C and Derek Eamus DA School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
B Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia.
C The Fenner School of Environment and Society, Australian National University, Canberra, ACT 0200, Australia.
D Institute for Water and Environmental Resource Management and Department of Environmental Sciences, University of Technology, Sydney, NSW 2007, Australia.
E Corresponding author. Email: d.a.pepper@unsw.edu.au
F This paper originates from a presentation at EcoFIZZ 2007, Richmond, New South Wales, Australia, September 2007.
Functional Plant Biology 35(6) 493-508 https://doi.org/10.1071/FP08125
Submitted: 14 April 2008 Accepted: 4 June 2008 Published: 4 August 2008
Abstract
A simple process-based model was applied to a tall Eucalyptus forest site over consecutive wet and dry years to examine the importance of different mechanisms linking productivity and water availability. Measured soil moisture, gas flux (CO2, H2O) and meteorological records for the site were used. Similar levels of simulated H2O flux in ‘wet’ and ‘dry’ years were achieved when water availability was not confined to the first 1.20 m of the soil profile, but was allowed to exceed it. Although the simulated effects of low soil and atmospheric water content on CO2 flux, presumably via reduction in stomatal aperture, also acted on transpiration, they were offset in the dry year by a higher vapour-pressure deficit. A sensitivity analysis identified the processes that were important in wet versus dry years, and on an intra-annual timeframe. Light-limited productivity dominated in both years, except for the driest period in the dry year. Vapour-pressure deficit affected productivity across more of each year than soil moisture, but both effects were larger in the dry year. The introduction of a reduced leaf area tended to decrease sensitivity in the dry year. Plant hydraulic architecture that increases plant available water, maximises productivity per unit water use and achieves lower sensitivity to low soil moisture levels should minimise production losses during dry conditions.
Additional keywords: CO2 flux, drought, evapotranspiration, water flux, water use.
Acknowledgements
D. A. Pepper, R. E. McMurtrie and B. E. Medlyn acknowledge financial support from the Australian Research Council and the Australian Government Department of Climate Change. We are grateful to Ray Leuning and Steve Zegelin at CSIRO, Australia, for the provision of soil moisture and flux data. We are grateful for support provided by TERACC (NSF Grant No. 0090238) for a modelling workshop held in Cronulla, Sydney, Australia, in 2006.
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