CONCENTRATION-DEPENDENT EFFECTS OF OZONE ON TRANSLOCATION OF ASSIMILATES IN DOUGLAS-FIR

The assessment of air quality standards for forest ecosystems requires proper knowledge about concentration-effect relations of air pollutants for tree species. In this study, 2-yr-old Douglas fir seedlings [Pseudotsuga menziesii (Mirb.) Franco] were exposed to 23, 81, and 169 mu-g O3/m3 during 8 h/d, 5 d/wk for a period of 4 wk. After exposure, the trees were placed in an atmosphere containing 14CO2. Release of 14CO2 in the root/soil compartment was analyzed once a day and was regarded as an index of transport and utilization of C-14 photosynthates. Respiratory release of C-14 was temporarily inhibited by O3 during the first days following exposure to the air pollutant. Within 2 wk after the O3 treatment, 14CO2 in the root/soil respiration was the same in all treatments, indicating that trees were recovering from O3 injury.