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Halman, Joshua M.

Rubenstein School of Environment and Natural Resources

2007

M.S.

Considerable evidence has shown significant losses of soil calcium (Ca) from eastern forests over the last fifty years due to acid deposition, soil-aluminum (Al) mobilization, nitrogen (N) saturation, a reduction in atmospheric base cation inputs, intensive forest harvesting, and changing climatic conditions that may accelerate natural acidifying processes. Such losses reduce the availability of this essential nutrient to trees, and may predispose them to significant changes in productivity and health. Because Ca is implicated in a host of stress response processes, reductions in its availability could impair signal transduction in times of environmental stress, thereby jeopardizing the stress tolerance of trees. A unique setting in which to study the effects of Ca depletion on tree health is the Hubbard Brook Experimental Forest in Thornton, NH, where Ca depletion has been documented and monitored for decades, and where one of the many small watersheds in the forest has been fertilized with a form of Ca to simulate prepollution levels of Ca availability. Recent research documented that red spruce (Picea rubens Sarg.) trees from the Ca addition watershed experienced significantly less winter injury than trees from a reference watershed in 2003 - a high injury year. My research examines whether or not changes in Ca nutrition affect key physiological and stress response processes in native red spruce, and if these changes may be in part responsible for differences in winter injury previously documented. Current-year foliage from red spruce in both a biogeochemical reference watershed, and the Ca-addition watershed, were collected in November 2005 and February 2006, analyzed, and compared for their cation nutrition, soluble sugar concentrations, ascorbate peroxidase (a key antioxidant enzyme) activity, and cold tolerance.
Ca content and total sugar concentration were significantly greater in foliage of trees from the Ca addition watershed during both fall and winter (P = 0.037, 0.035 for November; P = 0.055,0.036 for February, respectively). Individual sugar concentrations of fructose and glucose in November (P = 0.013,0.007, respectively), and sucrose in winter (P = 0.005), were also found to be significantly greater in foliage from the Ca addition watershed. Ascorbate peroxidase activity was similar in trees from both watersheds in fall (P = 0.278), but greater in the Ca addition watershed during winter (P = 0.063). Additionally, the cold tolerance of foliage from the Ca addition watershed was significantly greater than that from the reference watershed (P <0.001). These differences indicate that ambient Ca depletion suppressed sugar accumulation and APX activity needed for adequate cold tolerance development. The suppression of these Ca-dependent processes likely predisposed red spruce on the reference watershed to greater winter injury in 2003. Because the reference watershed reflects ambient forest conditions in the region, the consequences of impaired physiological function due to Ca-depletion may have more widespread implications for forest health.