Variations In Soil N Cycling And Trace Gas Emissions In Wet Tropical Forests

We used a previously described precipitation gradient in a tropical montane ecosystem of Hawai'i to evaluate how changes in mean annual precipitation (MAP) affect the processes resulting in the loss of N via trace gases. We evaluated three Hawaiian forests ranging from 2200 to 4050 mm year-1 MAP with constant temperature, parent material, ecosystem age, and vegetation. In situ fluxes of N2O and NO, soil inorganic nitrogen pools (NH4+ and NO3-), net nitrification, and net mineralization were quantified four times over 2 years. In addition, we performed 15N-labeling experiments to partition sources of N2O between nitrification and denitrification, along with assays of nitrification potential and denitrification enzyme activity (DEA). Mean NO and N2O emissions were highest at the mesic end of the gradient (8.7+/-4.6 and 1.1+/-0.3 ng N cm-2 h-1, respectively) and total oxidized N emitted decreased with increased MAP. At the wettest site, mean trace gas fluxes were at or below detection limit (