Acidic deposition has depleted calcium (Ca) from soils in northeastern forests. Calcium plays a vital role in forest tree growth and productivity. It modulates many cellular activities, including: ionic balance needed for stomatal closure, turgor pressure regulation, gene expression, carbohydrate metabolism, and cell division. Calcium silicate (wollastonite) was added to watershed 1 of the Hubbard Brook Experimental Forest in October 1999 to study its effects on various aspects of ecosystem function. The present report concerns species-specific elevation-dependent effects of Ca supplementation on ‘soluble’ (i.e. dilute acid extractable) foliar metabolites (polyamines, amino acids, proteins, and chlorophyll) and, inorganic ions in red spruce, sugar maple, yellow birch, and American beech. Polyamines are organic cations that are needed for growth and development. In most forest tree species, putrescine, one of the three common polyamines is often inversely correlated with soil and/or foliar soluble Ca.

Results/Conclusions The foliar soluble Ca content increased significantly in all hardwood species in response to Ca supplementation; the maximum increase was seen in sugar maple at mid elevation (550-650 m). Accompanying this were concurrent increases in chlorophyll, glutamic acid and glycine, and a significant decrease in the diamine putrescine (whose elevated level in foliage is a biochemical marker of stress from various environmental factors including Ca deficiency) in sugar maple trees at mid elevation. No changes were observed in foliar putrescine or Ca in sugar maple or yellow birch at low elevation. However, an increase in chlorophyll did occur in all hardwoods at low elevation indicating an indirect benefit of Ca addition. Putrescine levels at high elevation were lower only in sugar maple, suggesting a recovery from possible Ca deficiency. Since the type of positive physiological response that accompanied the increase foliar Ca in sugar maple was not observed for yellow birch or American beech, it can be argued that either the soil Ca thresholds were adequate for these two species, or they have more efficient Ca uptake mechanisms than sugar maple. A positive relationship for most soil and foliar inorganic ions was observed in this study. These results reinforce and extend earlier observations of sugar maple decline associated with Ca depletion in the northeastern United States. They also show sugar maple is more sensitive to decreases in soil Ca compared to yellow birch and American beech. Additionally, they further our understanding of the physiological processes that may be involved in this decline.