PARENT SESSION
Contributed Oral Session 110: Biogeochemistry: Nitrogen Dynamics
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 513 C, Level 5, Palais des congrès de Montréal

Large-scale manipulations of forest floor litter result in an increase in litter P inputs of a wet tropical forest in Costa Rica.

Wood, Tana^*,1, Lawrence, Deborah¹, Clark, Deborah², ¹ Department of Environmental Sciences, Charlottesville, VA, 22902² Department of Biology, St. Louis, MO, 63121

ABSTRACT- Litter induced pulses of nutrient availability could play an important role in phosphorus (P) cycling of wet tropical forests. We hypothesized that (1) an increase in both the quantity and quality of litter inputs would feed back positively on leaf litter P cycling and (2) the timing of this response would be influenced by both soil fertility and land use history. To test these hypotheses, we established a large-scale litter manipulation experiment in secondary and mature forests of varying soil fertility at La Selva Biological Station, Costa Rica. Leaves and twigs <2cm in diameter were removed from a 400m² area and added to an adjacent area of 100m². This transfer was equivalent to adding 100-200g of P per m². We established two replicates of the removal and addition treatments, plus a control plot at six locations (2 secondary, 2 mature-high fertility, 2 mature-low fertility). We analyzed leaf litter mass and 'P' in the three treatments over a 2-yr period. Overall, litter addition resulted in a significant increase in both leaf litter mass and P input 4-5 months following litter application (RANOVA: (litter) F=4.04, P=0.0276, (P input) F=5.57, p=0.0085). The increase in P input ranged from 30-40%. The sites with intermediate values of litter P addition (200-250 g/m²) showed the strongest response to litter addition (Tukey-Kramer). Neither litter treatment or forest type influenced temporal variation in litter mass and P, indicating that environmental factors are likely driving this variation. Our results suggest that seasonal variation in leaf litter mass and 'P' could result in a positive feed back on leaf litter P cycling.

Key words: phosphorus, litter, tropical forest, nutrient cycling