Auca

Abstract: Dendrochemical and biochemical markers link stress in apparently healthy red spruce trees (Picea rubeits) to acidic deposition. Acidic deposition to spruce forests of the northeastern USA increased sharply during the 1960s. Previous reports related visible damage of trees at high elevations to root and soil processes. In this report, dendrochenlical and foliar biocllemical markers indicate perturbations in biological processes in healthy red spruce trees across the northeastern USA. Previous research on the dendrochemistry of red spruce ste~nwood indicated that under uniform environmental conditions, stemwood concentrations of Ca and Mg decreased with increasing radial distance from the pith. For nine forest locations, frequency analysis shows that 28 and 52% of samples of red spruce stemwood formed in the 1960s are enriched in Ca and Mg, respectively, relative to wood formed prior to and after the 1960s. This enrich~nent in trees tllroughont the northeastern USA may be interpretable as a signal of increased availability of essential cations in forest soils. Such a temporary increase in the availability of Ca and Mg could be caused by cation mobilization, a consequence of increased acidic deposition. During cation mobilization, essential Ca and Mg as well as potentially harnlful Al become more available for interaction with binding sites in the soil and absorbing roots. As conditions which favor cation nlobilization continue, Ca and Mg can be leached or displaced from the soil. A nleasure of the interaction between Ca and Al is the AUCa binding ratio (molar charge ratio of exchangeable Al to exchangeable Ca). As the AUCa binding ratio in the root zone increased from 0.3 to 1.9, the foliar concentration of the biochen~ical stress marker putrescine also increased from 45 to 145 nm g-.'. The correlation of the pntrescine concentration to the AUCa binding ratio (adj. r" 0.68, P < 0.027) suggests that foliar stress may be linked to soil chenlistry. the mobilization of harmful A1 in high elevation watersheds of the northeastern USA was associated with the atmospheric deposition of nitric and sulfuric acid (Cronan and Schofield, 1979). This mobilization of A1 was described as a possible cause for the deterioration of forest canopies, and death of red spruce trees in these same watersheds (Hertel, 1988).