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Olszyk, D., M. Johnson, D. Tingey, G. King, M. Storm and M. Plocher. 2003. Effects of carbon dioxide and ozone on growth and biomass allocation in Pinus ponderosa. Ekológia (Bratislava) 22(sup.1):265-276. WED-02-164

The future productivity of forests will be affected by combinations of elevated atmospheric CO2 and O3. Because productivity of forests will, in part, be determined by growth of young trees, we evaluated shoot growth and whole-plant biomass responses for Pinus ponderosa seedlings exposed to ambient or elevated CO2 (+ 269 ppm above ambient) and low or high O3. The seedlings were grown under the CO2 and O, treatments for three years in sun-lit chambers with ambient temperature and humidity. A native forest soil from under a mature P. ponderosa stand was used with a soil moisture regime reflecting a wet winter/dry summer pattern. Elevated CO2 increased stem diameters over the course of the study. At the final harvest, elevated CO2 produced an increase in biomass for structural components of the seedlings, especially stems, buds and 2-10 mm diameter roots; but not for other plant components. There was only a tendency for an increase in total plant biomass at the final harvest, and no significant effect of CO2 on relative biomass allocation among plant components and organs. Ozone reduced the stimulatory effect of elevated CO2 on stem diameter early during the study when N and soil moisture may not have been limiting, but at the final harvest there were no significant O} effects or O3 x CO2 interactions for total biomass or any biomass component This study indicated the potential for CO2, but not O3, effects on tree seedlings under realistic field conditions; i.e., P. ponderosa seedlings grown for several years at low N in their native soil, at low soil moisture in the summer, and with relatively low cumulative O3 exposures.

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