Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Determinants of leaf litter nutrient cycling in a tropical rainforest: fertility versus topography.

Wood, Tana*,1, Lawrence, Deborah1, 1 University of Virginia, Charlottesville, VA

ABSTRACT- We were interested in the influence of landscape-level variation of soil fertility and topographic position on leaf litter nutrient dynamics in a neotropical rain forest in Costa Rica. We sampled across the three main soil types (ultisol slope, ultisol plateau, and inceptisol) to determine the effect of soil nutrients on leaf litter nutrient concentrations while controlling for topography, and to examine topographic effects while controlling for soil nutrients. Both leaf litter macronutrient (phosphorus (P), nitrogen (N), sulfur (S), calcium (Ca), potassium (K), magnesium (Mg)) and micronutrient concentrations were examined over a four-year period. All of the leaf litter macronutrients examined, with the exception of N, varied significantly among soil types. Variation in leaf litter [P] and [S] was explained by soil fertility alone. In contrast, [Ca] and [Mg] were influenced by topographic position, while [K] varied significantly with both soil fertility and topographic position. Macronutrients (P, K, Mg, S, Ca) were much less variable than less limiting nutrients such as Fe and Al. Lower variability in essential plant nutrients suggests a great deal of plant control over the amount of nutrients resorbed before senescense. Leaf litter macronutrient concentrations varied significantly over the 4-year sample period; however, the pattern did not differ among the three soil types as anticipated. Hence, while the magnitude of nutrient fluxes may be controlled by local factors such as soil fertility and topographic position, temporal changes are likely regulated by a common environmental variable such as precipitation.

Key words: Tropical, Phosphorus, Litter, Nutrient Cycling