Red spruce seedling health: an assessment of acid fog deposition and heavy metal soil contamination as interactive stress factors

Abstract

Two-year-old spruce (Picearubens Sarg.) seedlings were exposed to 12 treatment regimes of acid fog deposition and heavy metal soil amendment over a 2-year period. Seedling health was assessed by measuring five health indices, including general vigor estimate, height, diameter, bud number, and biomass (leaf, stem, and twig, and total). Soil was amended with cadmium, copper, lead, manganese, nickel, and zinc added in amounts comparable to high-elevation forest soils in the northeastern United States. Seedlings were also treated with simulated fog, with ionic chemistry similar to high-elevation northeastern fog events, adjusted to pH 3 or 5. The seedlings were planted in metal-amended soil and subjected to fog treatments in greenhouse chambers from August 6, 1986, to October 29, 1987, in weekly regimes of 30-h exposures. Of all the seedling stress factors imposed, only the lead amendment at 2000 ppm concentration, which is approximately 10 times the current ambient forest floor high-elevation level, had a consistently adverse impact on the seedling health parameters measured. Vigor rating of experimental seedlings was adversely impacted by precipitaton acidity in the absence of lead and other heavy metal soil amendments. Height, diameter, and live bud count of the seedlings were quite insensitive to treatment conditions. Treatment interactions were also generally unimportant.