ACIDIC DEPOSITION, CATION MOBILIZATION, AND BIOCHEMICAL INDICATORS OFSTRESS IN HEALTHY RED SPRUCE

Dendrochemical and biochemical markers link stress in apparently healt hy red spruce trees (Picea rubens) to acidic deposition. Acidic deposi tion to spruce forests of the northeastern USA increased sharply durin g the 1960s. Previous reports related visible damage of trees at high elevations to root and soil processes. In this report, dendrochemical and foliar biochemical markers indicate perturbations in biological pr ocesses in healthy red spruce trees across the northeastern USA. Previ ous research on the dendrochemistry of red spruce stemwood indicated t hat under uniform environmental conditions, stemwood concentrations of Ca and Mg decreased with increasing radial distance from the pith. Fo r nine forest locations, frequency analysis shows that 28 and 52% of s amples of red spruce stemwood formed in the 1960s are enriched in Ca a nd Mg, respectively, relative to wood formed prior to and after the 19 60s. This enrichment in trees throughout the northeastern USA may be i nterpretable as a signal of increased availability of essential cation s in forest soils. Such a temporary increase in the availability of Ca and Mg could be caused by cation mobilization, a consequence of incre ased acidic deposition. During cation mobilization, essential Ca and M g as well as potentially harmful Al become more available for interact ion with binding sites in the soil and absorbing roots. As conditions which favor cation mobilization continue, Ca and Mg can be leached or displaced from the soil. A measure of the interaction between Ca and A l is the Al/Ca binding ratio (molar charge ratio of exchangeable Al to exchangeable Ca). As the Al/Ca binding ratio in the root zone increas ed from 0.3 to 1.9, the foliar concentration of the biochemical stress marker putrescine also increased from 45 to 145 nm g(-1). The correla tion of the putrescine concentration to the Al/Ca binding ratio (adj. r(2) = 0.68, P < 0.027) suggests that foliar stress may be linked to s oil chemistry.