Abstract

The main sources of the low-molecular-weight aliphatic and aromatic organic acids (LMWOAs) in soils are plant residues, root exudates, and microbial metabolites. In the solutions of upper soil layers of forest ecosystems, citric, oxalic, and malic acids predominate among aliphatic LMWOAs, while substituted and unsubstituted benzoic and cinnamic acids predominate among aromatic LMWOAs. The LMWOA concentrations in plant tissues, root exudates, and microbial metabolites vary from several to some tens of millimoles per liter. In soil solutions, these values decrease by one–two orders of magnitude because of LMWOA sorption and biodegradation, their migration downward the profile, and dilution effect. The sorption of LMWOA anions increases with a decrease in pH and an increase in the concentrations of iron oxides/hydroxides and amorphous aluminosilicate clays. Polybasic acids are more tightly bound to solid phase as compared with monobasic acids. The sorption mechanisms vary depending on pH and LMWOA molecular structure and include formation of innersphere and outersphere surface complexes, ligand exchange, and cation bridge bond. Aromatic LMWOAs can be involved in a hydrophobic interaction. LMWOAs are very rapidly decomposed in the upper horizons, their lifespan amounting to several hours. Some important functions of LMWOAs in soils and landscapes are discussed, including their involvement in the global carbon cycle, mineral weathering, Al and Fe mobilization and translocation, mobilization of Fe and P compounds in the soils deficient in these elements, formation of acid–base buffering of natural waters, and detoxication of soils with increased contents of aluminum, heavy metals, and organic pollutants in soil solutions.

中文翻译：

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土壤中的低分子量有机酸：来源，组成，浓度和功能：综述

摘要

土壤中低分子量脂族和芳族有机酸（LMWOA）的主要来源是植物残渣，根系分泌物和微生物代谢产物。在森林生态系统的上层土壤层溶液中，柠檬酸，草酸和苹果酸在脂族低分子量甲基丙烯酸中占主导地位，而取代和未取代的苯甲酸和肉桂酸在芳香族低分子量甲基丙烯酸中占主导。植物组织，根系分泌物和微生物代谢产物中LMWOA的浓度范围从每升几毫摩尔到几十毫摩尔不等。在土壤溶液中，由于LMWOA的吸附和生物降解，它们向剖面下方的迁移以及稀释作用，这些值降低了1-2个数量级。LMWOA阴离子的吸附随着pH的降低以及铁氧化物/氢氧化物和无定形硅铝酸盐粘土浓度的增加而增加。与一元酸相比，多元酸与固相的结合更紧密。吸附机理取决于pH和LMWOA分子结构，包括内球和外球表面复合物的形成，配体交换和阳离子桥键。芳族LMWOA可参与疏水相互作用。LMWOA在高层被迅速分解，其寿命长达数小时。讨论了LMWOA在土壤和景观中的一些重要功能，包括它们参与全球碳循环，矿物风化，铝和铁的动员和转运，