Throughfall exclusion and leaf litter addition drive higher rates of soil nitrous oxide emissions from a lowland wet tropical forest

Tropical forests are a significant global source of the greenhouse gas nitrous oxide (N2O). Predicted environmental changes for this biome highlight the need to understand how simultaneous changes in precipitation and labile carbon (C) availability may affect soil N 2O production. We conducted a small-scale throughfall and leaf litter manipulation in a lowland tropical forest in southwestern Costa Rica to test how potential changes in both water and litter derived labile C inputs to soils may alter N 2O emissions. Experimentally reducing throughfall in this wet tropical forest significantly increased soil emissions of N 2O, and our data suggest that at least part of this response was driven by an increase in the concentration of dissolved organic carbon [DOC] inputs delivered from litter to soil under the drier conditions. Furthermore, [DOC] was significantly correlated w ith N 2O emissions across both throughfall and iitterfaii manipulation plots, despite the fact that native NOT pools in this site were generally small. Our results highlight the importance of understanding not only the potential direct effects of changing precipitation on soil biogeochemistry, but also the indirect effects resulting from interactions between the hydroiogic, C and N cycles. Finally, over ail sampling events we observed lower mean N 2O emissions ( < 1 ng N 2 0 -N cm ^^h^') than reported for many other lowland tropical forests, perhaps reflecting a more general pattern of increasing relative N constraints to biological activity as one moves from drier to wetter portions of the lowland tropical forest biome.