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

本研究的目的是描述无机N和C的形态之间的关系，并评估C作为N循环能量来源的重要性。在志贺县柳柳山同一龄柳杉人工林下沿坡样带进行了研究。土壤氮转化的地形变化；虽然氮矿化速率无显著差异，但不同坡位的硝化速率存在差异。斜坡下部的硝化与矿化比几乎为100%，而斜坡上部没有发生硝化。在坡体中部，高硝化和低硝化呈斑块状分布。土壤净氮转化的控制因素沿样带测定了土壤含水量、全碳、全氮、水分可提取有机碳、有机氮（如C和N）及pH值。原理分析表明，硝化作用是碳、氮和含水量的函数，而矿化作用是总碳和总氮的函数，说明硝化作用受有效底物控制，矿化作用受总底物调节。土壤总氮转化的控制因素采用15N稀释法研究土壤总氮转化。坡体下部总氮矿化和硝化作用较高，与土壤碳氮比较低一致。坡体上部呈现低矿化、低硝化、高C/N的特征，说明坡体下部低C/N条件下，C受到限制，以自养硝化为主。

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.