Distribution of nitrous oxide and regulators of its production across a tropical rainforest catena in the Luquillo Experimental Forest, Puerto Rico

Understanding of N2O fluxes to the atmosphere is complicated by interaction s between chemical and physical controls on both production and movement of the gas. To better understand how N2O production is controlled in the soil , we measured concentrations of N2O and of the proximal controllers on its production in soil water and soil air in a field study in the Rio Icacos ba sin of the Luquillo Experimental Forest, Puerto Rico. A toposequence (ridge , slope-ridge break, slope, slope-riparian break, riparian, and streambank) was used that has been previously characterized for groundwater chemistry and surface N2O fluxes. The proximal controls on N2O production include NO3 -, NH4+, DOC, and O-2. Nitrous oxide and O-2 were measured in soil air and NO3-, NH4+, and DO were measured in soil water. Nitrate and DOC disappeared from soil solution at the slope-riparian interface, where soil N2O concent rations increased dramatically. Soil N2O concentrations continued to increa se through the flood plain and the streambank. Nitrous oxide concentrations were highest in soil air probes that had intermediate O-2 concentrations. Changes in N2O concentrations in groundwater and soil air in different envi ronments along the catena appear to be controlled by O-2 concentrations. In general, N processing in the unsaturated and saturated zones differs withi n each topographic position apparently due to differences in redox status.