中文摘要：

研究土壤Mn（Ⅱ）释放规律对揭示锰氧化物的形成机制和了解酸性土壤锰毒效应大小具有重要意义.结果表明,柠檬酸溶解砖红壤过程中,Mn（Ⅱ）的释放速率在前4 h比较迅速,其释放数量可达24 h反应时间内总释放量的59.5%,但随后释放速率逐渐减缓.快速阶段被认为是土壤表面交换态Mn（Ⅱ）的释放,而慢速阶段则与土壤锰氧化物的缓慢溶解密切相关.低pH条件有利于Mn（Ⅱ）释放,其释放机制包含柠檬酸对土壤锰氧化物的还原-溶解.A l（Ⅲ）对Mn（Ⅱ）的释放有抑制作用,而Fe（Ⅲ）则有促进作用.有机酸的解离性质及官能团活性对Mn（Ⅱ）的释放有重要影响.在所研究的pH范围内,Mn（Ⅱ）释放数量按柠檬酸〉丙酮酸〉酒石酸〉苹果酸≈乳酸的顺序下降.此外,就草酸和柠檬酸比较而言,当pH值小于4.25,草酸体系中Mn（Ⅱ）释放数量大于后者,但随着pH升高,则表现出相反的规律.

英文摘要：

Knowledge of the mechanism of Mn（Ⅱ） release from soils is critical to elucidate the formation of Mn oxides and to assess the biotoxicity of excess Mn（Ⅱ） to plants in acid soils.As our results show,release of Mn（Ⅱ） during citric acid promoted dissolution of Latosol was characterized by an initial rapid reaction in which about 59.5% of total Mn（Ⅱ） released during 24h reaction time was discharged to solution.Following the rapid reaction,the rate of Mn（Ⅱ） release decreased significantly.The rapid release of Mn（Ⅱ） was attributed to the release of exchangeable Mn（Ⅱ） on the soil,and the slow stage was believed to be the dissolution of Mn oxides.The release of Mn（Ⅱ） was favorable at low pH through several mechanisms involving the reductive dissolution Mn（Ⅲ） or Mn（IV） oxides by citric acid.The presence of Al（Ⅲ） inhibited the release of Mn（Ⅱ）,while the release was enhanced after the addition of Fe（Ⅲ）.The ability of organic acids to promote Mn（Ⅱ） release from the soil followed the order： citric acid pyruic acid tartaric acid malic acid≈lactic acid.In addition,as far as citric acid and oxalic acid were concerned,the concentration of Mn（Ⅱ） in oxalic acid system was higher than that in citric acid system with pH below 4.25.However,the reverse trend was found after pH was increased.The result above indicated that dissociation of organic acids with the change in pH and the reactivity of function groups in their structures were significant to the release of Mn（Ⅱ） from the soil.