Spatial variations in nitrous oxide and nitric oxide emission potential on a slope of Japanese cedar (Cryptomeria japonica) forest

To quantify the spatial variation and spatial structure of nitrous oxide (N2O) and nitric oxide (NO) emission from forest soils, we measured N2O and NO emission rates from surface soil cores taken at 1 m intervals on a cross-line transect (65 m x 20 m) on a slope of Japanese cedar (Cryptomeria japonica) forest in a temperate region of central Japan and analyzed the spatial dependency of N oxide gas emissions using geostatistics. We divided N2O emission into N2O from denitrification and N2O from nitrification using the acetylene inhibition method. According to the geostatistical analysis, N2O emission rates on the slope had large spatial variation and weak spatial dependency. This weak spatial dependency was caused by the inordinately high N2O emissions on the slope, which were derived mainly from denitrification. In contrast, NO emission rate on the slope had large spatial variation, but strong spatial dependency and a distinct spatial distribution related to slope position, that is, high in the middle of the slope and low in the shoulder and the foot of the slope. The CN ratio and water-filled pore space were the dominant factors controlling NO emission rate on a slope. Our results suggest that spatial information about topographic factors helps to improve the estimation of both N2O emission and NO emission from forest soils.