Cloudwater and Ozone Effects upon High Elevation Red Spruce: A Summary of Study Results from Whitetop Mountain, Virginia
Thornton, F. C. | Joslin, J. D. | Pier, P. A. | Neufeld, H. | Seiler, J. R. | Hutcherson, J. D.
This paper integrates the results of a number of studies on the effects of cloudwater and ozone (O₃) on red spruce (Picea rubens Sarg.) seedlings, saplings, and mature trees at Whitetop Mountain, VA, over a 3-yr period. These investigations consisted of (i) seedling chamber exclusion studies, (ii) mature tree branch chamber exclusion studies, and (iii) field experiments comparing responses of seedlings, saplings, and mature trees. The studies included treatments that: (i) excluded clouds and O₃ (COE), (ii) excluded clouds and had ambient O₃ (CE), and (iii) exposed plants to both clouds and O₃ either with (CC) or without (AA) chambers. Seedlings and mature branches in the various treatments were compared with respect to growth rates, gas exchange rates, foliar nutrition, and chlorophyll and wax content. Soil solution, throughfall, and foliar responses of mature trees near the summit, receiving differing amounts of cloud exposure (low cloud and high cloud sites) were also monitored. Ozone was found to have minimal effects on the parameters measured, whereas cloudwater exposure was found to have adverse effects on several response parameters. Chambered seedlings that were exposed to cloudwater (AA and CC), and mature trees at the high cloud site had significantly lower foliar Ca and Mg concentrations than their counterparts, which were protected from exposure (seedlings) or received low cloud exposure (mature). A 3 to 5°C increase in cold tolerance was also measured in seedlings from which cloudwater was excluded. These findings suggest that cloudwater-mediated effects are currently having a negative impact on the health of red spruce, and may be involved in red spruce decline in the eastern USA.
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