Nitrate uptake enhanced by availability of dissolved organic matter in tropical montane streams

Tropical forests store large amounts of Earth’s terrestrial C, but many tropical montane streams have low dissolved organic matter (DOM). This availability energy likely limits certain pathways inorganic N uptake, as evidenced by the high rates nitrification and predominance nitrate (NO3−) in total pool seen forests. To explore influence DOM on stream cycling, we performed nutrient pulse additions NO3− with or without an added C source (acetate urea) Luquillo Experimental Forest, Puerto Rico. In absence DOM, uptake was either undetectable had very long (>3000 m) lengths (Sw). When NO3−, Sw values for were much shorter (97–1500 m), shortest resulting from acetate. Comparing metrics sources, there greater demand acetate compared to urea, measurable urea detected less frequently. During NO3−-only additions, ambient concentrations carbon (DOC) nitrogen (DON) decreased some cases, suggesting increased metabolic under elevated levels nutrients. Collectively, these results demonstrate that cycling are tightly tied at this site. The response DOC DON increases points important feedbacks between including N. Understanding controls processing is predicting network-scale exports ecosystems.