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PROCEEDINGS: Index of Abstracts


The atmospheric deposition of strong acid anions such as sulfate and nitrate shifts the ion exchange equilibrium in the rooting zone of sensitive forests. Red spruce and other northern coniferous forests are especially sensitive to deposition due to the shallow rooting of trees in a mor-type forest floor. Initially, the deposition of strong acid ions mobilizes essential cations such as calcium (Ca) from ion-exchange sites on soil organic matter. Hypothetically, this mobilization would result in a brief period of increased availability for root uptake. Evidence for this temporary period of increased uptake of essential Ca is the subject of this report. Radial trends in stemwood calcium concentration [Ca] occurred in a common pattern in two sample collections of red spruce from the northeastern United States and in one sample collection of Siberian fir from south-central Siberia, Russia. The [Ca] was measured in wood segments comprising rings that formed during 1871-90, 1891-1910, 1911-30, 1931-50, 1951-70 and 1971-90. For each core, the relative increase or decrease in [Ca] for consecutive periods of wood formation was determined. Previous research indicated that under equilibrium conditions, [Ca] in stemwood decreased in more recently formed wood due to declining numbers of Ca binding sites. Consistent with expectation, the relative frequency of positive change was low among most consecutive periods of growth. Contrary to expectation, however, the frequency of positive increases (48 percent) in [Ca] doubled in 1951-70 compared to 1931-50; this increased frequency was significantly greater (P < 0.01) than between all other periods.