OZONE EFFECTS ON GRAFTED MATURE AND JUVENILE RED SPRUCE - PHOTOSYNTHESIS, STOMATAL CONDUCTANCE, AND CHLOROPHYLL CONCENTRATION

Red spruce (Picea rubens Sarg.) was grown as grafted mature and juvenile scions in open-top chambers and exposed to charcoal-filtered air, nonfiltered air, and nonfiltered air with ozone additions of either 75 or 150 ppb above ambient to determine if tissue age affects the species response to oxidant pollution as measured by photosynthesis, stomatal conductance, and chlorophyll concentration. After 18 weeks of exposure th ozone of concentrations as high as 170 ppb (nonfiltered air + 150 ppb ozone) in an 8-h period, net photosynthesis of grafted red spruce was reduced by ozone. Significant reductions were not observed until September 1988. Mature and juvenile scions grown in nonfiltered air + 150 ppb ozone showed 29 and 40% reductions, respectively, in mean seasonal net photosynthesis (mg CO2.g dry wt.-1.h-1) compared with those plants grown in nonfiltered air. Scion age had a significant effect on net photosynthesis and stomatal conductance. Net photosynthesis (mg CO2.g dry wt.-1.h-1) and stomatal conductance were 38 and 47% higher, respectively, in juvenile than in mature scions. Chlorophyll a and total chlorophyll concentration of juvenile scion needles were significantly reduced 19 and 24%, respectively, when grown in nonfiltered air + 150 ppb ozone compared with that grown in charcoal-filtered air (p < 0.01). Mature scions had significantly more chlorophyll a than juvenile scions in October 1988. Current-year needles collected from mature scions had significantly greater mass, length, one-sided projected surface area, width, and thickness than juvenile scions. Mature scions had significantly lower needle numbers per centimetre branch than did juvenile scions. No differences in specific leaf weight were observed. Mature scions had less ozone uptake than did juvenile scions.