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Red Spruce Response to Ozone and Cloudwater after Three Years Exposure

Atmospheric Science Department, Tennessee Valley Authority, Chemical Engineering Building 2A, Muscle Shoals, AL 35660.

^* Corresponding author.

ABSTRACT

This study reports on the results of a 3-yr study conducted at a high elevation site in the southern Appalachians to determine if cloudwater and ozone (O₃) adversely affect the growth of red spruce seedlings (Picea rubens Sarg.). Field chambers were established at Whitetop Mountain, VA (elevation 1689 m), in 1988. Three replicate chamber treatments were constructed to produce the following treatments: (i) exclusion of clouds and O₃ (COE), (ii) ambient O₃ with clouds removed (CE), and (iii) exposure to both clouds and O₃ (CC). Ambient air plots (AA) were also included in order to assess possible chamber effects. Potted native seedlings from the surrounding forest and seedlings grown from seed collected in the Great Smoky Mountains National Park (GSM seedlings) were used in the study. After 3 yr, seedlings were impacted little by the reduction in pollution levels within the CE and COE chambers. No differences in seedling diameter growth were found for either seedling type, and height growth differences that were detected indicated more height growth in treatments with ambient O₃ and cloudwater. Minimal biomass effects were also found. Increased nutrient leaching of needle Ca and Mg was observed in cloudwater treatments, but needle concentrations were not reduced to deficiency levels. Removal of both cloudwater and O₃ (COE) did not enhance photosynthesis (Ps) rates for native or GSM seedlings. However, Ps of seedlings in which only cloudwater was removed (CE) was lower in 1-yr-old needles (C + 1) of native and GSM seedlings, and in 2-yr-old needles (C + 2) of native seedlings. These lower Ps rates of CE seedlings were correlated with lower needle N concentrations, indicating that cloudwater NO₃^– and NH₄⁺ may have provided a fertilizer effect within AA and CC treatments. Respiration of current year needles of native seedlings was not affected by treatments; however, respiration was lower in older needles (C + 1 and C +2) in which O₃ and cloudwater were removed (CE and COE).