Concentration ratios of aluminum to calcium, magnesium, and other divalent cations in increment cores obtained from red spruce and eastern hemlock trees growing in the Great Smoky Mountains National Park in Tennessee and North Carolina have increased in an unprecedented manner during the last 15–40 years. These trends, which also occur in other trees growing in eastern North America and Germany may reflect the mobilization of exchangeable aluminum by [Formula: see text] and [Formula: see text] deposition. The soil chemistry and plant physiology bases for this hypothesis are presented. Many of the spruce and hemlock cores from the Great Smoky Mountains also showed an inverse relationship between radial growth and aluminium:alcium ratios in the wood. Changes in the availability of soil cations, as recorded in tree rings, may provide an ecosystem-level method of evaluating the historical response of forest soils to atmospheric deposition.

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To assess seasonal and site variation in foliar nitrate reductase activity and its utility as a biochemical marker for the uptake of nitrogen oxide pollutants in high-elevation forests, we measured nitrate reductase activity in current-year needles of red spruce (Picearubens Sarg.) saplings at two high-elevation stands (1935 and 1720 m) in the Great Smoky Mountains, North Carolina. Measurements spanned two growing seasons between September 1987 and September 1988. Nitrate reductase activity peaked near 60 nmol•g−1•h−1 at both sites in September and October 1987 and August 1988 and declined 80% in November 1987 and 65% in September 1988. Although nitrate reductase activity was 30% greater in saplings at the higher site relative to the lower site in September and October 1987, activity dropped to approximately 10 nmol•g−1•h−1 at both sites in November 1987. No differences among sites were evident the following year. Comparing deposition of nitric acid vapor at a nearby site to nitrate reductase activity suggests that needle nitrate reductase activity is not an unequivocal marker for foliar uptake of nitrogen oxides during air pollutant episodes. The changes in soil nitrate levels in this system provide preliminary evidence that foliar nitrate assimilation may, in part, include nitrate taken up from the soil, as the highest activity occurred during periods of higher A-horizon nitrate concentrations in 1988. These measurements of nitrate reductase activity suggest that red spruce are capable of assimilating nitrate in foliage in the field and that the nitrate assimilation capacity varies throughout the year.

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Portions of this document may be illegible in electronic image products. Smages are pduced from the best avaible oFiginal document. PROJECT SUMMARYThree years of field research were conducted to evaluate biological and chemical indicators of the current and future health of the Southern Appalachian Spruce-Fir Ecosystem. The focus of this research has been on identification and understanding mechanisms through which current levels of acidic deposition are impacting ecosystem processes. Principal mechanisms and key biological indicators of change were examined to improve our capabilities to detect, monitor, and assess the effects of air quality regulations and attendant future air quality changes on ecosystem response. The research was organized into three Tasks: I. Nitrogen Deposition and Cycling; 11. Soil Chemistry and Plant Nutrition; and 111. Physiological Indicators of Plant Function.Studies on nitrogen deposition and cycling found that the forest canopy can either decrease or increase deposition to the forest floor. At a site below cloud base the canopy acted as a sink intercepting 83% of the incident ammonium and 34% of the incident nitrate. This significantly reduced nitrogen inputs to the forest floor compared to deposition in nearby gaps, which experienced greater hydrologic fluxes. Above cloud base increased canopy interception increased throughfal! and deposition. Resultant atmospheric inputs of nitrogen are generally higher above cloud base, however local topography and year to year meteorological conditions can significantly influence total deposition and the ratios of wet to dry deposition. 15N Tracer studies demonstrated that ammonium and nitrate are retained and incorporated by needles and stems of red spruce and Fraser fir saplings. Canopy retention by current-year needles was similar for NH, and NO,, similar between spruce and fir, and was found to range between 1 and 9% of the isotopic additions to individual trees. Over 76% of deposited nitrate and 55% of ammonium deposited on in situ soil cores was mobile, indicating a high potential for N deposition to increase cation leaching losses from these poorly buffered soils.Reduced calcium availability is apparently limiting growth of spruce and possibly fir at high elevation sites and recently analyzed survey data indicate reduced foliar levels of base cations, most notably calcium, at high elevations. Reduced ratios of foliar to soil cation levels indicated a reduced efficiency of cation uptake and/or retention likely related to increased acidic deposition at higher elevation sites. Fertilization of 25 two-tree plots of mature red spruce at Whitetop Mountain Virginia in 1990 and 1991 improved growth (+20%) of foliage, improved foliar Ca:Al ratios (-t20-60%), and continued to improved Ca:AI ratios in soil solutions three years after the last calcium application date. Similarly calcium additions to red spruce saplings on Clingman's Dome increased the efficiency of carbon metabolism, increased stem growth, and increased nitrogen uptake. Histochemical...