Fluxes of nitrogen and phosphorus in a gallery forest in the Cerrado of central Brazil

Abstract

The Gallery forests of the Cerrado biome play a critical role in controlling stream chemistry but little information about biogeochemical processes in these ecosystems is available. This work describes the fluxes of N and P in solutions along a topographic gradient in a gallery forest. Three distinct floristic communities were identified along the gradient: a wet community nearest the stream, an upland dry community adjacent to the woodland savanna and an intermediate community between the two. Transects were marked in the three communities for sampling. Fluxes of N from bulk precipitation to these forests resulted in deposition of 12.6 kg ha−1 y−1 of total N of which 8.8 kg ha−1 was as inorganic N. The throughfall flux of total N was generally <8.4 kg ha−1 year−1. Throughfall NO3–N fluxes were higher (7–32%) while NH4–N and organic N fluxes were lower (54–69% and 5–46%) than those in bulk precipitation. The throughfall flux was slightly lower for the wet forest community compared to other communities. Litter leachate fluxes differed among floristic communities with higher NH4–N in the wet community. The total N flux was greater in the wet forest than in the dry forest (13.5 vs. 9.4 kg ha−1 year−1, respectively). The stream water had total N flux of 0.3 kg ha−1 year−1. The flux of total P through bulk precipitation was 0.7 kg ha−1 year−1 while the mean fluxes of total P in throughfall (0.6 kg ha−1 year−1) and litter leachate (0.5 kg ha−1 year−1) declined but did not differ between communities. The low concentrations presented in soil solution and low fluxes in stream water (0.3 and 0.1 kg ha−1 year−1 for N and P, respectively) relative to other flowpaths emphasize the conservative nutrient cycling of these forests and the importance of internal recycling processes for the maintenance and conservation of riparian and stream ecosystems in the Cerrado.