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

大气氮沉降引起土壤酸化，但土壤有不同的酸缓冲反应。研究了杉木林下植被采收过程中氮动态、酸生成和缓冲反应的变化对凋落物风化和碱离子供应的影响。收获林下植被对氮和水分的吸收减少。收获期土壤温度的升高（收获区比未收获区高约2℃）影响了有机氮矿化和后续硝化作用的活性。这也是氮浸出增加的一个原因。此外，土壤温度升高导致凋落物层溶解有机碳供给量增加，也影响了矿化和硝化活动。氮浸出量的增加使产酸量因氮转化而增加。该产酸量在二氧化硅动员与其解释因素之间具有最高的相关系数。锶同位素比值（^<87>Sr /^<86>Sr）与二氧化硅浓度成负比例。由于与降雨和植物或土壤相比，矿物的Sr <87> / Sr <86>，因此风化作用应该有助于酸缓冲反应。我们还分析了萃取物的^<87>Sr/^<86>Sr，用于分析O层总钙和交换性钙（Ca）含量。从1层（未分解凋落物）到1层（腐殖凋落物）的比例增加。说明凋落物交换态钙的增加与凋落物重的减少不仅与非交换态钙的转化有关，还与降雨中的钙有关。由于0层钙的补给缓解了土壤酸化，我们应该尝试研究风化与钙补给之间的关系。

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.