Study on weathering that alleviate soil acidification due to atmospheric nitrogen deposition

大气氮沉降引起土壤酸化，但土壤有各种酸缓冲反应。本研究旨在探讨风化作用和凋落物分解对盐基阳离子供应的贡献，以了解采伐日本雪松林下植被引起的氮素动态、产酸和缓冲反应的变化。收获林下植被降低了对氮素和水分的吸收。收割引起的土壤温度升高(收割区比未收割区高约2℃)影响了有机氮矿化和随后的硝化作用的活性。这也是氮素淋失增加的一个原因。此外，由于土壤温度升高，0层(凋落物层)溶解有机碳供应量的增加也影响了土壤的矿化和硝化活性，氮素淋失量的增加导致了氮素转化产酸量的增加。产酸量与二氧化硅活化度及其解释因子的相关系数最高。锶同位素比值(^&lt；87&gt；sr/^&lt；86&gt；sr)与二氧化硅浓度呈负相关。由于与降雨、植物或土壤相比，矿物的^&lt；87&gt；sr/^&lt；86&gt；sr较低，因此风化作用应有助于酸性缓冲作用。同时对提取物进行了分析，分析了O层中总钙和交换性钙含量。从Oi层(未分解的凋落物)到Oe层(腐殖化的凋落物)，这一比例逐渐增加。这表明，凋落物中交换性钙的增加伴随着凋落物重量的减少，这不仅归因于非交换性钙的转化，而且归因于降雨中钙的转化。由于0层钙的供应缓解了土壤酸化，因此我们应该尝试研究风化与钙供应之间的关系。

Atmospheric nitrogen deposition causes soil acidification but soils have various acid buffer reactions. We aimed to examine contribution of weathering and supplies of base cations owing to litter decomposition based on changes in nitrogen dynamics, acid production, and buffering reaction due to reaping understory vegetation under Japanese cedar (Cryptomeria japonica). Reaping understory vegetation decreased in uptake of nitrogen and water. Increase in soil temperature owing to reaping (about 2℃ higher in reaping area than in un-reaping area) affected on activities of mineralization of organic nitrogen and subsequent nitrification. This was also a cause of increases in nitrogen leaching. In addition, increase in supplies of dissolved organic carbon from 0 horizon(Litter layer)due to increase in soil temperature also affected on activities of mineralization and nitrification.Increases in nitrogen leaching made increase in acid production due to nitrogen transformation. This acid production had the highest correlation coefficient between silica mobilization and its explanatory factors. Strontium isotope ratio (^<87>Sr /^<86>Sr) was negatively proportional to silica concentration. Since minerals have lower^<87>Sr/^<86> Sr, compared rainfall and plants or soils, weathering should contribute to acid buffering reaction. We also analyzed^<87>Sr/^<86>Sr of extracts, which analysis for total and exchangeable calcium (Ca) contents in O horizon. The ratio increased from Oi horizon (not decomposed litters) to Oe horizon (humified litters). It suggested that increase in exchangeable Ca in litter accompanied with decrease in litter weight would be ascribed to not only transformation from non-exchangeable form but to Ca in rainfall. Since supplies of calcium from 0 horizon alleviate soil acidification, we should try to examine relationship between weathering and supplies of Ca.