Tuesday, 8 November 2005 - 2:30 PM
193-5

Linkages among Soil, Foliar and Litter Chemical Response to Experimentally Elevated N and S Deposition at the Bear Brook Watershed in Maine.

Lindsey E. Rustad, USDA Forest Service, 35 Crystal Lane, Cumberland, ME 04021 and Ivan Fernandez, University of Maine, 5722 Deering Hall, Orono, ME 04469-5722.

Risks to forest health and productivity due to elevated atmospheric N and S deposition remain a scientific priority and policy concern. The Bear Brook Watershed in Maine is a long-term, whole-ecosystem manipulation experiment in which bimonthly aerial applications of (NH4)2SO4 have been applied to one of two paired forested watersheds (~10 ha each) since 1989, that currently results in a 3X and 2X loading above ambient for N and S, respectively. Long-term research at this site demonstrated that, after 8 years, experimentally elevated N and S additions increased N mineralization by 22% and decreased soil exchangeable Ca and Mg content by 32 and 54%, respectively . The increased N availability resulted in significantly elevated foliar N concentrations (15, 29, and 9% for American beech, sugar maple, and red spruce respectively) in the treated compared to the reference watershed. Although considerable N was resorbed from foliage prior to senescence, foliar litter N concentrations were also higher (by 27, 28, and 17% for beech, maple, and red spruce, respectively) in the treated compared to the reference watershed. The decline in soil exchangeable base cations did not strongly influence foliar Ca and Mg concentrations but did result in a significant concentration decline of 12 and 32% for Ca for beech and spruce litter, respectively, and 29, 21, and 40% for Mg in beech, maple, and spruce litter respectively, suggesting a greater conservation of these nutrients during senescence in the treated than the reference watershed. Correlation analysis showed that foliar and litter N concentrations were most highly correlated with measures of N mineralization. Foliar and litter Ca and Mg concentrations were generally positively correlated to measures of soil base cation status and negatively correlated to measures of total acidity. Overall, results demonstrated the linkages between soil, foliar, and litter chemistry at this site.


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