Determinants of Leaf Litter Nutrient Cycling in a Tropical Rain Forest: Soil Fertility Versus Topography Tana E. Wood, 1 * Deborah Lawrence, 1 and Deborah A. Clark 2 1 Department of Environmental Sciences, University of Virginia, P O Box 400123, Charlottesville, Virginia 22904-4123, USA; 2 Department of Biology, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, Missouri 63121, USA ABSTRACT We investigated the influence of landscape-level variation in soil fertility and topographic position on leaf litter nutrient dynamics in a tropical rain forest in Costa Rica. We sampled across the three main edaphic conditions (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 nutri- ents. Both leaf litter macronutrient [phosphorus (P), nitrogen (N), sulfur (S), calcium (Ca), potas- sium (K), magnesium (Mg)] and micronutrient concentrations were quantified throughout a 4-year period. Leaf litter [P], [N] and [K] varied significantly among soil types. The variation in [P], [N], and [K] was explained by soil fertility alone. Leaf litter [S], [Ca], and [Mg] did not vary among the three soil types. Macronutrient (P, K, Mg, S, Ca) concentrations in the leaf litter were much less variable than those of 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 con- centrations varied significantly over the 4-year period, but the temporal variation did not differ among the three edaphic types as anticipated. Hence, although the magnitude of nutrient fluxes may be controlled by local factors such as soil fertility, temporal patterns are likely regulated by a common environmental variable such as precipita- tion or temperature. Key words: cations; edaphic; leaf litter; nutrients; phosphorus; soil fertility; topography; tropical rain forest. INTRODUCTION On a global scale, patterns of nutrient cycling differ considerably among tropical sites with contrasting soil fertility (Vitousek and Sanford 1986). In gen- eral, an increase in soil fertility is positively associated with leaf litter quality, nutrient con- centrations in live leaf tissue, decomposition rates, and nitrogen mineralization (Edwards 1982; Vito- usek and Sanford 1986; Crews and others 1995; Vitousek 1988; Aerts and Chapin 2000). In addi- tion, nutrient availability plays an important role in the ability of plants to withstand environmental stress. High nutrient levels contribute to main- taining osmotic pressure in leaves, enabling plants to withstand a higher degree of drought stress (Murphy and Lugo 1986). Therefore, soil fertility should affect both the magnitude and, depending on the degree of drought stress experienced, the temporal pattern of nutrient flow through leaf lit- terfall at the landscape scale. Topography can also affect leaf litter nutrient cycling. Soil moisture and cation exchange capacity tend to be lower on steep slopes than on plateaus (Becker and others 1988; Silver and others 1994; Received 14 February 2005; accepted 14 September 2005; published online 8 August 2006. *Corresponding author; e-mail: tana@virginia.edu Ecosystems (2006) 9: 700–710 DOI: 10.1007/s10021-005-0016-7 700