Spatiotemporal variation in N2O flux within a slope in a Japanese cedar (Cryptomeria japonica) forest

Abstract

Topographic factors affect nitrogen cycling in forest soils, including nitrous oxide (N2O) emissions, which contribute to the greenhouse effect. We measured the N2O flux at 14 chambers placed along a 65-m transect on a slope for 1 year at 2- to 3-week intervals. We applied a hierarchical Bayesian model with a conditional autoregressive (CAR) model to assess the spatiotemporal N2O flux along a slope and quantify the effects of environmental factors on N2O emissions. N2O fluxes at chambers located at lower positions along the slope were relatively greater than those at higher positions. During the non-soil-freezing period, N2O fluxes fluctuated seasonally depending on soil temperature. The soil temperature dependency of N2O fluxes at each chamber increased with descending slope position (the median of the Q10 equivalent simulated from posterior distribution ranged from 1.18 to 3.64). According to the Bayesian hierarchical model, this trend could be partially explained by the C/N ratio at each chamber position. During the soil-freezing period, relatively high N2O fluxes were observed at lower positions along the slope.