Friday, August 10, 2007
Exhibit Halls 1 and 2, San Jose McEnery Convention Center
Acidic deposition has depleted calcium (Ca) from soils in northeastern forests. Calcium silicate (wollastonite) was added to watershed 1 (WS1) of the Hubbard Brook Experimental Forest in October 1999 to study its effects on various aspects of ecosystem function. In the present study, changes in foliar physiology of red spruce (at high elevation only) and hardwoods (sugar maple, yellow birch, and American beech at three different elevations) were studied in order to evaluate the effects of Ca addition on stress physiology. The effects of Ca addition were species-specific and varied with elevation. In general, the physiology at high elevation was significantly different from low elevation. Putrescine, a positively charged diamine, has been shown to be an indicator of foliar and/or soil Ca deficiency in several tree species. Even though soluble Ca in all hardwoods foliage significantly increased with Ca addition, foliar physiology of sugar maple was most sensitive to this addition. At mid to high elevations, an increase in Ca lowered free putrescine in the foliage of sugar maple indicating remediation from stress caused by Ca deficiency. A lack of inverse relationship between putrescine and Ca at low elevation suggests the absence of Ca deficiency at this elevation. However, the increase observed in total chlorophyll, glutamic acid, and glycine in sugar maple at low and mid elevations was caused by positive indirect effects of Ca addition on soil base cation status and mycorrhizal associations as reported previously. A decrease in putrescine with an increase in foliar Ca, as seen in our study with sugar maple at high elevation, does not necessarily imply that all other limiting factors for growth such as soil nutrients, light, temperature, and altitude have been relieved. Significantly lower putrescine in SM as compared to other species indicates highest sensitivity of this species to Ca deficiency.
