Carbon and nitrogen relationship in soil N Transformation of a forest ecosystem

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The objectives of this study are to describe the relationship between the form of inorganic N and C and to evaluate the importance of C as energy source for N cycling. We studied the transect along a slope under the same aged Cryptomeria plantation in Mt. Ryuoh, Shiga prefecture.1. Topographical variation of soil N transformation ; Although there was no significant difference in N mineralization rate, nitrification rate was different between the positions of the slope. Nitrification ratio to mineralization was almost 100% at the lower slope, while no nitrification occurred at the upper part of the slope. At the middle part of the slope, patchy distribution of high nitrification and low nitrification was shown.2. Controlling factor of net soil N transformation ; Soil moisture content, total C and N, water extractable organic C and N (ex. C and N) and pH were investigated along the transect. The principle analysis showed nitrification was the function of ex. C, ex. N and moisture content, while mineralization was the function of total C and N.it indicated that nitrification was controlled by available substrate, mineralization was regulated by total substrate.3. Controlling factor of gross soil N transformation ; Gross soil N transformation was investigated by using 15N dilution method. The high gross N mineralization and nitrification were shown at the lower part of the slope, It was consistent with the low soil C/N.At the upper part of the slope, low mineralization, low nitrification and high soil C/N was shown, It suggests that C is limiting under low C/N at the lower part of the slope and autotrophic nitrification dominated.