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

本研究的目的是阐明茎流和树根分泌物中所含有机酸在铝解毒中的作用，铝解毒对植物生长有各种影响。红木（Chamaecyparis obtusa）茎流的pH、EC、TOC和离子平衡数据表明，初始茎流的pH、EC、TOC和离子平衡值与散装样品不同，茎流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了它们在茎流中的含量可以忽略不计。茎流中所含的有机阴离子可能是来源于树皮成分的各种酚类物质。通过土壤萃取试验，评价了茎流中有机物的络合能力。结果表明，茎流没有额外的离子提取。然而，由于茎流中存在多种高分子有机物质，因此仍存在有机质在茎流中络合作用的可能性。测定了铝对库鲁奇根系有机物排泄量的影响。Al处理后培养液中TOC浓度低于对照。有机物质排泄的抑制不是由于缺乏磷、钙等营养物质引起的，而是由直接铝效应引起的。另一方面，添加铝后，柠檬酸和苹果酸的排泄量有增加的趋势。综上所述，根际铝的存在使有机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.