Predicting ozone-induced reduction of carbon sequestration of forests under elevated tropospheric ozone concentrations requires robust mechanistic leaf-level models, scaled up to whole tree and stand level. As ozone effects depend on genotype, the ability to predict these effects on forest carbon cycling via competitive response between genotypes will also be required. This study tests a process-based model that predicts the relative effects of ozone on the photosynthetic rate and growth of an ozone-sensitive aspen clone, as a first step in simulating the competitive response of genotypes to atmospheric and climate change. The resulting composite model simulated the relative above ground growth response of ozone-sensitive aspen clone 259 exposed to square wave variation in ozone concentration. This included a greater effect on stem diameter than on stem height, earlier leaf abscission, and reduced stem and leaf dry matter production at the end of the growing season. Further development of the model to reduce predictive uncertainty is discussed.
Bibliographical noteFunding Information:
We would like to extend our thanks to M.D. Coleman, A. Sober, E. McDonald and A. Noormets for useful discussions on aspen data and W. Zhao for programming support. We acknowledge Steve Long and Steve Humphries for background information on the formulation of the model WIMOVAC. Work on the original ozone model was funded by the Natural Environmental Research Council, UK, under grant GT4/92/16/L; initial parameterization of the model for aspen clones was funded by a grant to the University of Essex, from Brookhaven National Laboratory. Development of the ECOPHYS project was funded jointly by the Computational Biology Program of the National Science Foundation, Grant No. DBI-972395, the Northern Global Change Program of the USDA Forest Service, and the U.S. Department of Energy under interagency agreement No. DE-A105-800R20763. Additional funding came from the NSF/DOE/NASA/USDA Joint Program on Terrestrial Ecology and Global Change through a cooperative agreement with Michigan Technological University. This is Contribution No. 296 of the Center for Water and the Environment, Natural Resources Research Institute, University of Minnesota, Duluth, MN.