Shigihara Ado, Matsumoto Kiyoshi, Sakurai Naoki, Igawa Manabu
Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, Yokohama, Japan.
Sci Total Environ. 2008 Jul 15;398(1-3):185-95. doi: 10.1016/j.scitotenv.2008.03.007. Epub 2008 May 2.
Virgin fir forests have been declining since the 1960s at Mt. Oyama, which is located at the eastern edge of the Tanzawa Mountains and adjacent to the Kanto plain in Japan. An acid fog frequently occurs in the mountains. We collected throughfall and stemflow under fir trees and rainfall every week during January-December 2004 at Mt. Oyama to clarify the influence of acid fog on the decline of fir (Abies firma) needles. In relation to throughfall and stemflow, D-mannose, D-galactose, and D-glucose are the major neutral sugar components; only D-glucose is a major component of rainfall. The correlation coefficient between the total neutral sugars and uronic acid (as D-galacturonic acid), which is a key component of the cross-linking between pectic polysaccharides, was high except for rainfall. The leached amount of calcium ion, neutral sugars, uronic acid, and boron is related to the nitrate ion concentration in throughfall. Results of a laboratory exposure experiment using artificial fog water simulating the average composition of fog water observed at Mt. Oyama (simulated acid fog: SAF) on the fir seedling needles also shows a large leaching of these components from the cell walls of fir needles. The leaching amount increased concomitantly with decreasing pH of the SAF solution. We also observed that a dimeric rhamnogalacturonan II-borate complex (dRG-II-B) that exists in the cell wall as pectic polysaccharide was converted to monomeric RG-II (mRG-II) by the leaching of calcium ion and boron. Results not only of field observations but also those of laboratory experiments indicate a large effect of acid depositions on fir needles.
自20世纪60年代以来，位于日本丹泽山脉东缘、毗邻关东平原的小御岳山上的冷杉林一直在减少。山区经常出现酸雾。2004年1月至12月期间，我们每周在小御岳山收集冷杉树下的穿透雨和茎流以及降雨，以阐明酸雾对冷杉（日本冷杉）针叶衰退的影响。关于穿透雨和茎流，D - 甘露糖、D - 半乳糖和D - 葡萄糖是主要的中性糖成分；只有D - 葡萄糖是降雨的主要成分。除降雨外，总中性糖与作为果胶多糖交联关键成分的糖醛酸（以D - 半乳糖醛酸计）之间的相关系数很高。钙离子、中性糖、糖醛酸和硼的淋溶量与穿透雨中的硝酸根离子浓度有关。使用模拟小御岳山观测到的雾水平均组成的人工雾水（模拟酸雾：SAF）对冷杉幼苗针叶进行的实验室暴露实验结果也表明，这些成分从冷杉针叶细胞壁中大量淋溶出来。淋溶量随着SAF溶液pH值的降低而增加。我们还观察到，作为果胶多糖存在于细胞壁中的二聚鼠李半乳糖醛酸聚糖II - 硼络合物（dRG - II - B）通过钙离子和硼的淋溶转化为单体RG - II（mRG - II）。野外观测结果和实验室实验结果均表明酸沉降对冷杉针叶有很大影响。
