Spatial variability of soil nitrogen transformation patterns along a forest slope in a Cryptomeria japonica D. Don plantation

Spatial variability of soil nitrogen (N) transformation patterns was investigated along a slope of a Cryptomeria japonica plantation. The controlling factors of the soil N transformation patterns were examined by multivariate analysis. Net N mineralization showed no clear gradient along the slope, while net nitrification and percent nitrification were high in the lower part, and very low in the upper part of the slope. The middle part was the transition zone corresponding to the patchiness of the lower and upper soils. Soil properties (e.g. C/N ratio and pH) except total N significantly correlated with slope position. Principal component (PC) analysis showed soil properties to be divided into three groups which were PC1 (water content and extractable organic C and N), PC2 (C/N ratio and pH), and PC3 (total C and N). Regressions of soil N transformation pattern against PCs scores suggested that net N mineralization was mainly regulated by PC3, while net nitrification and percent nitrification were mainly regulated by PC1 and PC2. The scatter plots of percent nitrification and the first two PCs scores suggest that PC2 regulates the potentiality, and PC1 affects specially in the middle of the slope where the effect of PC2 was moderate.