『Abstract
　Most previous studies investigating controls on nitrous oxide (N2O) emissions have relied on plot-scale experiments and focused on relative homogeneous biotic and abiotic factors such as soil, vegetation, and moisture. We studied soil N2O flux at 11 chamber sites along a 620 m topographic gradient in upstate New York, USA, aiming at identifying patterns of N2O flux and correlating them to hydrological factors and soil substrate properties along the gradient. The topographic gradient is a complex slope with an overall gradient of 8%, covering plant communities of pasture, forest, alfalfa field, and riparian area from the top to the bottom. Mean fluxes of N2O measured from late March to May ranged from 4.45 to 343 μg N m^-2 h^-1, and these fluxes were not significantly different among chamber sites located in different communities. With the descending of the slope, N2O fluxes increased with the increase of soil water content, except for the riparian site. Statistically, N2O fluxes were not strongly correlated with soil temperature, soil bulk density, and water filled pore space (p＞0.05). Instead, strong correlations (p＜0.05) were found between N2O fluxes and soil C and N content including NO3^-, NH4⁺, total organic carbon, and C/N ratio. Multiple linear regression analyses including both soil physical and substrate properties highlighted the significance of soil NO3^- content and C/N ratio in regulating N2O fluxes along the gradient.

Keywords: Greenhouse gases; Soil carbon; Soil nitrogen; Global climate change; Spatial variation』

1. Introduction
2. Materials and methods
　2.1. Site description
　2.2. N2O flux measurement
　2.3. Measurement of soil temperature and moisture
　2.4. Soil sampling and laboratory analysis
　2.5. Statistical analysis
3. Results
　3.1. Soil characteristics
　3.2. N2O flux
　3.3. Environmental controls and N2O flux
4. Discussion
Acknowledgements
References