Behavior of organic acids and their importance on detoxication of aluminum in soils in forest ecosystem

本研究旨在阐明树干茎流和树根分泌物中含有的有机酸在铝的解毒中所起的作用，铝对植物生长有不同的影响。Hinoki(Chamaecyparis Obtusa)茎流量的pH、EC、TOC和离子平衡数据表明，初始茎流量的值与散样不同，茎流量中含有一些有机阴离子。然而，低分子有机酸的分析结果证实，它们在茎流中的含量可以忽略不计。推测树干茎流中含有的有机阴离子是来源于树皮成分的各种酚类物质。通过土壤提取实验，评价了有机物在树干径流中的络合能力。结果表明，没有观察到树干流对离子的额外萃取。然而，由于树干茎流中存在多种高分子有机物，因此有机物质在树干茎流中发挥络合作用的可能性仍是可望的。铝处理后发酵液中总有机碳浓度低于对照。有机质排泄的抑制不是由磷、钙等营养物质的缺乏引起的，而是由铝的直接作用引起的。添加Al后，柠檬酸和苹果酸的排泄量有增加的趋势。由此可见，根际土壤中的铝导致有机物质的排泄量随物种的不同而增加或减少。

The purpose of this research is to clarify the role organic acids contained in stem flow and a secretion from tree root with respect to the detoxication of aluminum, which has various effects on plant growth.The data of pH, EC, TOC and ion balance in the stemflow of Hinoki (Chamaecyparis obtusa) show that those values of the initial stemflow were different from those of bulk samples and that the stemflow contains some organic anions. However, the results from the analysis of low molecular oorganic acid comfirmed that their contents in the stemflow were negligible. It was sugested that the organic anions contained in stemflow were various phenol substances originated from the bark constituents. The complexation abilityof organic substances in stemflow was evaluated by extraction experimentusing soils. As the results, no extra extraction of ions by using stemflow was observed. However, the possibility of complexation role of organic substancesin the stemflow was still expected because of the existence of various high molecular organic substances in the stemflow.The excretion of organic substances from roots of Kunugi (Quercus serrata Thumb) affected by aluminum was measured. The TOC concentration in the culture solution after Al treatments was lower that of control. The suppression of excretion of organic substance was not caused by deficiency of nutrients such as P or Ca but by direct Al effect. On the other hand, The tendency of the increase in the excretion of citric acid and malic acid was observed by Al addition. Therefore, it is concluded that Al in rhizospher causes the excretion of organic substances to both increase and decrease depending on the species.