A canopy-scale test of the optimal water-use hypothesis

STANISLAUS J. SCHYMANSKI, MICHAEL L. RODERICK, MURUGESU SIVAPALAN, LINDSAY B. HUTLEY & JASON BERINGER

Plant, Cell and Environment, 2008, 31, 97-111, doi: 10.1111/j.1365-3040.2007.01740.x

Abstract

Common empirical models of stomatal conductivity often incorporate a sensitivity of stomata to the rate of leaf photosynthesis. Such a sensitivity has been predicted on theoretical terms by Cowan and Farquhar, who postulated that stomata should adjust dynamically to maximize photosynthesis for a given water loss. In this study, we implemented the Cowan and Farquhar hypothesis of optimal stomatal conductivity into a canopy gas exchange model, and predicted the diurnal and daily variability of transpiration for a savanna site in the wet–dry tropics of northern Australia. The predicted transpiration dynamics were then compared with observations at the site using the eddy covariance technique.The observations were also used to evaluate two alternative approaches: constant conductivity and a tuned empirical model. The model based on the optimal water-use hypothesis performed better than the one based on constant stomatal conductivity, and at least as well as the tuned empirical model. This suggests that the optimal water-use hypothesis is useful for modelling canopy gas exchange, and that it can reduce the need for model parameterization.

Original Publication

Please download from http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-3040.2007.01740.x or send an email to sschym at bgc-jena.mpg.de.

Corrections

Equations (1) and (4) are missing a minus sign in the exponent. Equation (1) should be: J=Jmax*(1-e^(-0.3*Il/Jmax)). The same correction has to be made to the first term in Equation (4).

Data and Model Code

The data used for the model run was measured as part of the Fluxnet Project and is subject to the Fluxnet data use policy that can be found under http://www.fluxnet.ornl.gov/fluxnet/datapolicy.cfm or http://www.fluxdata.org/DataInfo/default.aspx. Please contact the principal investigator of the Howard Springs site (Dr. Jason Beringer) if you wish to use the data. The contact details and more information about the data and the site can be found under http://www.arts.monash.edu.au/ges/research/climate/fire/index.php.

For the purpose of reproducing the results presented in the associated publication, you can find the data used in the below table. The code used to convert the data and generate the results is given, too. Please note that the code contains additional computations and plots not addressed in the publications. Neither I nor anyone else guarantees the correctness of any of the data offered for download on this site. However, should you encounter problems or have questions, feel free to send an email to sschym at bgc-jena.mpg.de.

You need the software Mathematica by Wolfram or Mathematica Player to view and evaluate the code. Mathematica Player can be downloaded for free from http://www.wolfram.com/products/player.