PARENT SESSION
Poster Session #19: Nutrient Cycling.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Do nitrogen budgets explain soil nitrogen mineralization rate differences between oak-pine and northern hardwood stands?

Bonito, Gregory¹, Haines, Bruce¹, Coleman, David¹, ¹

ABSTRACT- Nitrogen mineralization rates typically decrease with decreasing temperature. Temperature decreases with increasing elevation. Thus, N-mineralization rates are expected to decrease with increasing elevation. However, soil N-mineralization rates at the Coweeta Hydrologic Lab, N.C. are higher at the highest elevation. Causes of higher N-mineralization rates at the higher elevation have yet to be explained. Alternative hypotheses to explain higher N-mineralization rates at the higher elevation, Northern Hardwoods (NH) compared to the Oak-Pine (OP) include: 1) a mineralization promoter in decomposing herbs, leaf litter or soil of the high elevation, 2) low pH in OP soils inhibiting N-mineralization, 3) differences in total nitrogen pools, 4) low moisture limitation in OP soils, 5) differences in soil texture, and 6) differences in biological communities. Previous studies did not support our N-mineralization promoter hypothesis, nor does soil pH explain mineralization rates. Presently we are exploring N-budget models for the NH and OP sites to see if differences in nitrogen pools and fluxes are sufficient to explain differences in N-mineralization rates. Evaluating N in the upper 10 cm of mineral soil, annual canopy litterfall, understory herb turnover, rainfall, canopy throughfall, and soil solution, NH has more stored nitrogen and greater nitrogen fluxes than OP. Why nitrogen storages and fluxes are greater in the NH is not obvious.

KEY WORDS: nitrogen, mineralization, soils, budgets