Nutrient status and winter hardiness of red spruce foliage

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Abstract
Increased ecosystem loading with inorganic nitrogen compounds derived from anthropogenic sources has been proposed to prolong vegetative growth of spruce, rendering them more susceptible to winter injury. Severely nutrient-deficient 4-year-old red spruce (Picea rubens Sarg.) seedlings and adequately fertilized seedlings were provided with synthetic cloud water lacking or containing nitrate, ammonium, or both, for a full growing season, and then exposed to normal winter chilling. Needles from these seedlings were stressed at -25 or -30.degree.C, and freezing injury was measured as ion leakage. Cloud water condensates had no effect on hardiness of needles of either nutrient status. Initially nutrient-sufficient seedlings transferred to nutrient-deficient conditions also exhibited no change in hardiness. Severely nutrient-deficient seedlings had needles that were significantly more sensitive to winter injury than seedlings under nutrient-sufficient conditions. Improving the nutrient status of initially nitrogen-deficient seedlings reduced their sensitivity to freezing injury. Based upon experimental results and consideration of the amounts of inorganic nitrogen reaching upper-elevation conifer forests, there is no evidence to support the hypothesis that anthropogenic nitrogen supplies significantly reduce winter hardiness of spruce foilage. It is improbable that winter injury due to elevated anthropogenic nitrogen is a causal factor in contemporary forest decline.