Photosynthesis
Leaf Response
Growth Response
Pest Interactions
Soil Response
Ozone Modeling

Objective:  A process-based model to predict the effects of ozone on photosynthesis was incorporated within an up-dated version of ECOPHYS to investigate whether the observed relative ozone-induced changes in partitioning in aspen clone 259 could be simulated from changes at the leaf level.

Introduction:

Predictions of ozone-induced reduction of carbon sequestration of forests under elevated tropospheric ozone concentrations require robust mechanistic leaf-level models scaled to the whole tree and stand level. This study tests a process-based model that predicts the effects of ozone on the photosynthetic rate of an ozone-sensitive aspen clone when scaled to the whole tree level, as a first step in the process of simulating the competitive response of genotypes to atmospheric and climate change.

 Model components:

Genotype: Aspen clone 259

Results

Model simulations of the relative growth response of ozone-sensitive aspen clone 259 under ozone exposure, compared with the charcoal filtered treatment, reflect the trends reported by Karnosky and co-workers (1996). In particular, the model showed that: 

1. stem dry matter production and stem diameter are dramatically reduced by ozone, while the effect on stem height was small;
2. ozone-induced earlier leaf abscission dramatically reduces both leaf dry matter production and retained leaf area, but with little or no effect on the number of leaves initiated.

These results corroborate earlier experimental findings (Coleman et al 1995) that the above-ground response of ozone-sensitive aspen to ozone exposure can be accounted for by the direct effects of ozone on photosynthesis. 

Acknowledgements

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 US 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 co-operative agreement with Michigan Technological University. 
 

Literature Cited

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Host, G. E.,  G. W. Theseira, C. Heim, J. G. Isebrands and R. Graham. 1999. EPIC-ECOPHYS: A linkage of empirical and process models for simulating poplar plantation growth. In: (A. Amaro and M. Tome Eds.) Empirical and Process Models for Forest Tree and Stand Growth Simulation.  Edicos Salamandra pp. 419-429.

Karnosky, D.F., Gagnon, Z.E., Dickson, R.E., Coleman, M.D., Lee, E.H., Isebrands, J.G., 1996. Changes in growth, leaf abscission, and biomass associated with seasonal tropospheric ozone exposures of Populus tremuloides clones and seedlings. Canadian Journal of Forestry Research 26, 23-37.

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The Northern Forest Ecosystem Experiment (NFEE) is funded by the US Forest Service. The Aspen FACE Experiment is funded principally by the U.S. Department of Energy's Office of Biological and Environmental Research. Additional support is from the USFS Global Change Program, Michigan Technological University, the Canadian Forest Service and the USFS Northern Research Station.