Laboratory and field ecophysiological studies on the impact of air pollution on red spruce and Fraser fir

Three studies were performed to investigate the impact of air pollution on high-elevation red spruce-Fraser fir forests in the Southern Appalachians.

In the first study, red spruce (Picea rubens Sarg.) and Fraser fir (Abies fraseri (Pursh.) Poir.) seedlings were submitted to long-term (2.5 yrs), multiple growing cycle (4 and 5, respectively), intermittent ozone fumigations (0.025, 0.070, and 0.150 ppm). No effect of ozone exposure on growth and gas exchange of the seedlings was found. Net photosynthesis at saturating light intensity was reduced in both species and the light compensation point was shifted upwards in spruce when exposed to ozone. Fraser fir seedlings showed inconsistent responses of CO₂ curve parameters to ozone exposure. There were indications that ozone exposure modified cell wall modulus of elasticity in both species.

In the second study, the impact of summer exposure to ambient pollutants on winter hardiness in red spruce seedlings was examined. The seedlings were subjected to the following summertime treatments while kept in exclusion chambers on the top of Whitetop Mountain (Virginia): ambient air and clouds, ambient air with clouds excluded, charcoal filtered air, and chamberless control treatment. During the following winter the seedlings were placed in Blacksburg (Virginia), in two locations: in the open and in a shadehouse. A number of conducted tests indicated that there were significant differences in winter damage between the chamber treatments and chamberless control, as well as between the winter exposure locations. Among the summer chamber exposure regimes, the treatment excluding clouds seemed to perform the best (although not all the evidence supports the latter statement).

In the third study, the physiology of red spruce trees of various sizes (seedlings, saplings, and overstory trees), growing on two sites on the top of Whitetop Mtn., was compared and related to ambient ozone concentration. Some seedlings were treated with an antioxidant EDU, to help evaluate the impact of ozone on their physiology. The trees of various sizes showed clear differences in gas exchange, with overstory trees photosynthesizing at the lowest rates, and seedlings - at the highest. Overstory trees also showed more negative shoot water potential and higher night respiration than smaller tree sizes. No deleterious effects of ambient ozone on red spruce physiology were detected.