© 2000 Heron Publishing—Victoria, Canada
Use of a single-tree simulation model to predict effects of ozone and drought on growth of a white fir tree
W. A. Retzlaff (1, 4), M. A. Arthur (2), N. E. Grulke (3), D. A. Weinstein (1) and B. Gollands (1)
1. Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, NY 14853-1801, USA / 2. Department of Forestry, University of Kentucky, Lexington, KY 40546, USA / 3. USDA, Forest Service, Pacific Southwest Research Station, 4955 Canyon Crest Drive, Riverside, CA 92507, USA / 4. Environmental Science Program, Box 1099, Southern Illinois University Edwardsville, Edwardsville, IL 62026-1099, USA (wretzla@siue.edu) / Received January 29, 1998
Summary
A physiologically based, single-tree simulation model, TREGRO, was parameterized with existing phenological, allometric, and
growth data and used to predict effects of ozone and drought on growth of a 53-year-old white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.) tree following a 3-year model simulation. Multiple experimental simulations were conducted to assess the individual
and interactive effects of ozone (O3) exposure and drought on growth of white fir. The effects of O3 were imposed as reductions in carbon (C) assimilation of 0, 2.5, 5, 10, and 20%. Drought was imposed as 0, 10, 25, and 50%
reductions in total annual precipitation. The results of the simulations were compared with the effects of O3 on white fir seedlings grown in the presence and absence of ozone in open-top chambers and with a field survey of white fir
trees subjected to a gradient of O3.
In the O3 simulations, an O3-induced reduction in C assimilation of 2.5% reduced total tree biomass and branch total nonstructural carbohydrate (TNC)
content by < 7%. Although quantifiable in simulation experiments, such small reductions would probably not be detectable in
the field. Results from both an open-top chamber experiment and a field survey indicated that reductions in C assimilation
of white fir growing in elevated O3 were much greater than 2.5%, but were not statistically different from control values. A simulated O3 reduction in C assimilation of ≥ 10% reduced total tree biomass by 7% and branch TNC by 55%. Results from the field survey
indicated that branch elongation was reduced in response to increased O3 concentration, corroborating the simulated response of reduced C allocation to the branches of white fir.
Although simulated reductions in total annual precipitation of ≥ 25% reduced final tree biomass, the simulated reductions
also reduced O3 uptake and therefore reduced the O3 response of white fir. However, a combination of low amounts of O3 (2.5% reduction in C assimilation) and drought (25% reduction in annual precipitation) synergistically reduced C gain of
white fir more than either stress individually. Our simulations predict that moderate drought (no more than a 25% reduction
in total annual precipitation) may not ameliorate the response of white fir to O3 and that moderate amounts of atmospheric O3 and drought could be more detrimental to white fir than either stress singly.
Keywords:
Abies concolor, carbon acquisition, carbon allocation, field survey, open-top chamber, total nonstructural carbohydrate, TNC, TREGRO.
