Li Jiuyu, Xu Renkou, Xiao Shuangcheng, Ji Guoliang
Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing, People's Republic of China.
J Colloid Interface Sci. 2005 Apr 15;284(2):393-9. doi: 10.1016/j.jcis.2004.10.051.
Low-molecular-weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes, such as nutrient availability, translocation of metals, fate of heavy metals, and mineral weathering. In this paper, the effect of the LMW organic anions on the exchangeable aluminum of two variable-charge soils was examined. The results showed that the organic anions induced an increase or a decrease in the exchangeable Al, and the extent and direction of the effect depended on the nature of organic anions, surface chemical properties of soils, and pH. For example, at pH 4.5, the quantity of exchangeable Al of Oxisol in the control system was 2.65 mmol kg(-1), whereas the values in the citrate, oxalate, malonate, malate, tartarate, salicylate, and lactate systems increased by 3.25, 1.93, 1.95, 1.82, 1.28, 0.88, and 0.45 times, respectively. In contrast, the quantity of the exchangeable Al of Ultisol at pH 4.5 in the oxalate and the citrate systems decreased by 8.8 and 19.6%, respectively. The increase in the exchangeable Al was caused mainly by the increase in negative surface charge of the soils due to the specific adsorption of organic anions. The ability of organic anions at low concentrations to increase exchangeable Al for Oxisol followed the order citrate > oxalate and malonate > malate > tartarate > salicylate > maleate > lactate. This order is consistent with that of the effect of the adsorption of anions on the increase in the negative surface charge and/or the decrease in the positive surface charge of the soil. On the other hand, the organic anions could depress the exchangeable Al through the formation of soluble Al-organic anion complexes under certain conditions. The anions with small stability constants of Al-organic anion complexes, such as lactate, caused an increase in exchangeable Al with the change in surface charge of the soils, while those with large stability constants, such as citrate and oxalate, caused an increase in the exchangeable Al at low concentration and a decrease at high concentration.
低分子量（LMW）有机酸广泛存在于土壤中，并与许多土壤过程有关，如养分有效性、金属迁移、重金属归宿和矿物风化。本文研究了低分子量有机阴离子对两种可变电荷土壤交换性铝的影响。结果表明，有机阴离子会导致交换性铝增加或减少，其影响程度和方向取决于有机阴离子的性质、土壤表面化学性质和pH值。例如，在pH 4.5时，对照体系中氧化土的交换性铝含量为2.65 mmol kg(-1)，而在柠檬酸盐、草酸盐、丙二酸盐、苹果酸盐、酒石酸盐、水杨酸盐和乳酸盐体系中，该值分别增加了3.25、1.93、1.95、1.82、1.28、0.88和0.45倍。相反，在pH 4.5时，在草酸盐和柠檬酸盐体系中，老成土的交换性铝含量分别下降了8.8%和19.6%。交换性铝的增加主要是由于有机阴离子的特异性吸附导致土壤表面负电荷增加。低浓度有机阴离子增加氧化土交换性铝的能力顺序为：柠檬酸盐＞草酸盐和丙二酸盐＞苹果酸盐＞酒石酸盐＞水杨酸盐＞马来酸盐＞乳酸盐。该顺序与阴离子吸附对土壤负表面电荷增加和/或正表面电荷减少的影响顺序一致。另一方面，在一定条件下，有机阴离子可通过形成可溶性铝-有机阴离子络合物来降低交换性铝。铝-有机阴离子络合物稳定性常数较小的阴离子，如乳酸盐，会随着土壤表面电荷的变化导致交换性铝增加，而稳定性常数较大的阴离子，如柠檬酸盐和草酸盐，则会在低浓度时导致交换性铝增加，在高浓度时导致交换性铝减少。
