In order to determine the primary causes of coniferous fine root damage and disfunction in acidic soils, hydroponic cultures of young spruce in pH neutral, acidic, and metal ion-amended media were established. After five months, physiological stress in the roots was removed by raising the pH in the acid and metal ion-amended cultures to physiological neutrality. The cellular element analytical techniques of x-ray microprobe (EDXA) and laser-micromass-spectroscopy (LAMMA) were applied to samples of various tissues of the cultured spruce. Nutrient uptake by the fine roots was blocked by the following ions in order of decreasing severity: A13+ > H + > Fe 3+ > Mn 2+ . Magnesium uptake by the fine root apoplast was greatly inhibited by these blockers as was calcium. A13+ and Fe 3+ act predominantly in the root cortex, while Mn 2+ is mobile throughout the whole plant. Besides the roots, nutrient deficiencies are also severe in the shoot bark and needles. Phloem processes might therefore be affected. The ion exchange functions of the fine roots are almost reversed by raising the pH of the solutions; the nutrient cations may then again be taken up by the apoplast and the crown status improved. The consequences of these findings are discussed with regard to soil processes and fertilization (liming) treatments under field conditions.

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