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

Net primary productivity and nitrogen mineralization in mesic and xeric deciduous forest stands.

Newman, Gregory¹, Arthur, Mary¹, Muller, Robert¹, ¹

ABSTRACT- Nitrogen availability and soil texture are thought to influence the productivity of temperate forests, although the relative importance of these factors in controlling above- and belowground productivity remains unclear. Above- and belowground net primary productivity and soil nitrogen mineralization were estimated on four paired mesic and xeric upper slopes, which occur on the same substrate at opposing slope aspects. Xeric stands have lower soil moisture (p<0.01) and are dominated by Quercus spp., while mesic stands are mixed deciduous. We predicted greater productivity and nitrogen mineralization on mesic stands based on differences in soil moisture and species composition. Despite greater litter mass (p=0.06) and LAI (p=0.05) on mesic stands, total foliar nitrogen and NPP were not statistically different between aspects. NPP ranged from 12.7 to 15.6 t ha^-1 yr^-1 in mesic stands and 13.8 to 19.4 t ha^-1 yr^-1 in xeric stands. ANPP was positively correlated with nitrogen mineralization (R²=0.51; p=0.05), but this relationship was lost for NPP (R²=0.03; p=0.68). This is attributed to higher proportional allocation of productivity belowground on stands with lower soil moisture and nitrogen mineralization. This trend was more dramatic on xeric stands. Further, higher nutrient-use efficiency in xeric stands with low nitrogen mineralization is driven by low nitrogen return in litterfall, suggesting a positive feedback between species' internal cycling and soil nutrient availability.

KEY WORDS: net primary productivity, nitrogen mineralization, carbon allocation, nutrient-use efficiency