Dissolved Nitrogen, Phosphorus, and Sulfur forms in the Ecosystem Fluxes of a Montane Forest in Ecuador

• Published in: Biogeochemistry 2006, Vol.77 (1), p.57-89
• Main Authors: Goller, R, Wilcke, W, Fleischbein, K, Valarezo, C, Zech, W
• Format: Article
• Language: English
• Subjects: ammonium nitrogen; Animal and plant ecology; Animal, plant and microbial ecology; Anthropogenic factors; biogeochemical cycles; Biological and medical sciences; dissolved organic carbon; dissolved organic nitrogen; dissolved organic phosphorus; dissolved organic sulfur; Earth sciences; Earth, ocean, space; Exact sciences and technology; Forest ecosystems; Forest soils; forested watersheds; Fundamental and applied biological sciences. Psychology; Leachates; Leaching; losses from soil; Mineral soils; Montane forests; Mountain forests; nitrate nitrogen; nitrogen; organic nitrogen compounds; Organic soils; organic sulfur compounds; organophosphorus compounds; phosphates; phosphorus; Rain; Rainfall; Rainstorms; Soil pH; Soil solution; Soil water; Soils; Stemflow; Stream discharge; Stream water; Streams; sulfates; Sulfur; Surficial geology; Synecology; Terrestrial ecosystems; Throughfall; Tropical forests
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-005-1061-1

The N, P, and S cycles in pristine forests are assumed to differ from those of anthropogenically impacted areas, but there are only a few studies to support this. Our objective was therefore to assess the controls of N, P, and S release, immobilization, and transport in a remote tropical montane forest. The study forest is located on steep slopes of the northern Andes in Ecuador. We determined the concentrations of NO₃-N, NH₄-N, dissolved organic N (DON), PO₄-P, dissolved organic P (DOP), SO₄-S, dissolved organic S (DOS), and dissolved organic C (DOC) in rainfall, throughfall, stemflow, lateral flow (in the organic layer), litter leachate, mineral soil solution, and stream water of three 8-13 ha catchments (1900-2200 m a.s.l.). The organic forms of N, P, and S contributed, on average, 55, 66, and 63% to the total N, P, and S concentrations in all ecosystem fluxes, respectively. The organic layer was the largest source of all N, P, and S species except for inorganic P and S. Most PO₄ was released in the canopy by leaching and most SO₄ in the mineral soil by weathering. The mineral soil was a sink for all studied compounds except for SO₄. Consequently, concentrations of dissolved inorganic and organic N and P were as low in stream water (TDN: 0.34-0.39 mg N l⁻¹, P not detectable) as in rainfall (TDN: 0.39-0.48 mg N l⁻¹, P not detectable), whereas total S concentrations were elevated (stream water: 0.04-0.15, rainfall: 0.01-0.07 mg S l⁻¹). Dissolved N, P, and S forms were positively correlated with pH at the scale of soil peda except inorganic S. Soil drying and rewetting promoted the release of dissolved inorganic N. High discharge levels following heavy rainstorms were associated with increased DOC, DON, NO₃-N and partly also NH₄-N concentrations in stream water. Nitrate-N concentrations in the stream water were positively correlated with stream discharge during the wetter period of the year. Our results demonstrate that the sources and sinks of N, P, and S were element-specific. More than half of the cycling N, P, and S was organic. Soil pH and moisture were important controls of N, P, and S solubility at the scale of individual soil peda whereas the flow regime influenced the export with stream water.