Organic acids, vitamins, and carbohydrates represent important organic compounds in soil. Aliphatic, cyclic, and aromatic organic acids play important roles in rhizosphere ecology, pedogenesis, food-web interactions, and decontamination of sites polluted by heavy metals and organic pollutants. Carbohydrates in soils can be used to estimate changes of soil organic matter due to management practices, whereas vitamins may play an important role in soil biological and biochemical processes. The aim of this work is to review current knowledge on aliphatic, cyclic, and aromatic organic acids, vitamins, and carbohydrates in soil and to identify directions for future research. Assessments of organic acids (aliphatic, cyclic, and aromatic) and carbohydrates, including their behaviour, have been reported in many works. However, knowledge on the occurrence and behaviour of D-enantiomers of organic acids, which may be abundant in soil, is currently lacking. Also, identification of the impact and mechanisms of environmental factors, such as soil water content, on carbohydrate status within soil organic matter remains to be determined. Finally, the occurrence of vitamins in soil and their role in biological and biochemical soil processes represent an important direction for future research.
Organic acids, vitamins, and carbohydrates play an important role in soil. Organic acids (aliphatic, cyclic, and aromatic) play key roles in rhizosphere ecology, pedogenesis, nutrient acquisition, allelochemical interactions, availability and detoxification of aluminium and pollutants, regulation of soil pH, enzymatic activities, and in food-web interactions [
Carbohydrates represent dominant compounds of plant root exudates. They play an important role in the establishment and functioning of mycorrhizal symbioses and the stabilisation of heavy metals in soil [
While there is little knowledge on occurrence of vitamins in soil, vitamins are known to play a number of important roles in plants including resistance to pathogens, plant-microbe symbioses, microbial growth stimulation, and stimulation of organic pollutant degradation [
A wide range of organic acids has been found in soil. These include aliphatic acids such as acetic, citric, isocitric, fumaric, tartaric, oxalic, formic, lactic, malic, malonic, butyric, succinic,
Knowledge of the behaviour of aliphatic organic acids in soil in terms of nutrient acquisition by plants, microbial degradation and adsorption, their role in pedogenesis and in Al detoxification, extraction, and analysis was reviewed by Jones [
Dominant organic acids in soil of different ecosystems.
Management | Dominant organic acids | Ratio aliphatic/cyclic plus aromatic acids | Concentrations | Sampling | Increase/decrease with depth | References |
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Citric, acetic, formic, oxalic, malic, butyric, propionic, malonic, lactic, tartaric, succinic, shikimic, and propionic acid | 4–157 | Up to 5820 |
Whole profile | Mostly decrease, sometimes increase with depth | [ |
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Citric, acetic, formic, lactic, and oxalic acid | 4–10 | Up to 1 |
A-horizon | — | [ |
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Contaminated soils (industrial, agricultural) | Oxalic acid | — | Up to 3 |
— | — | [ |
*Dissolved organic matter was extracted from the fresh A horizon soil samples using double-deionized water with a solid/volume ratio of 1 : 2.
Concentrations of aliphatic organic acids commonly decrease with soil depth, except in the case of some ecosystems such as those containing podzolized soils, where organic acids (e.g., formic acid) reportedly increased in concentration with depth [
Organic acids are involved in the formation of complexes of Al and Fe. The amount of complexed Al and Fe declines with soil depth [
The primary production rate of organic acids in different types of soils was predicted to be within the range of between <1 and 1250 nmol/g soil/d [
Organic acids were found to increase the activity of acid phosphomonoesterase in soil at low concentrations (<1
Average respiration rates of organic acids (oxalate, citrate) were reported to be around 209 nmol/g soil/d, and respiration of organic acids increased with soil depth [
There is a paucity of literature on organic acid enantiomers, but what does exist points to the need for urgent study. Liao et al. [
Organic acids play an important role in the phytoremediation of polluted soils and in the availability of heavy metals and organic compounds. Mobilisation of polycyclic aromatic hydrocarbons (PAHs) such as pyrene or phenanthrene by organic acids (citric, oxalic, tartaric, lactic, or acetic) is dependent on the type of organic acid, pH, and soil organic matter content [
Introduction of
Organic acids such as citric and tartaric acids were found to reduce Cr(VI) to Cr(III) in the soil [
Generally, citric acid is the most effective in terms of desorption of different heavy metals, followed by malic > acetic > tartaric > oxalic acid (Cu, Hg, Pb, Cd, Zn, and 137Cs) [
Huang et al. [
Organic acids appeared to be efficient in the release of 137Cs from contaminated soils, efficiency being in the order citric > tartaric > oxalic > succinic > acetic acid [
Cyclic and aromatic organic acids play a range of roles in soils, including allelopathic interactions, inhibition of microbial growth, and weathering of minerals [
Aromatic acids (salicylic and phthalic) are adsorbed by soils of different charges, and the adsorption of these acids differs significantly according to the soil tested. Adsorption of aromatic and aliphatic acids decreased the zeta potential of soils and oxides [
Inderjit and Bhowmik [
Cyclic and aromatic organic acids affect availability of heavy metals in soils. Whereas salicylic acid decreased availability of Pb, the presence of phthalic or salicylic acid increased the capacity of exchangeable Al. In some of the tested soils, salicylic acid decreased the capacity due to its lower adsorption and its formation of soluble Al-salicylate complexes [
Some aromatic acids, such as gallic acid, are efficient in extraction of heavy metals (Cd, Cu, Zn, and Ni) [
Glucose, galactosamine, fructose, rhamnose, arabinose, fucose, glucosamine, galactose, xylose, mannose, ribose, mannosamine, muramic, galacturonic, and glucuronic acids have all been identified in soil [
Adsorption of carbohydrates, such as glucose or fructose, on alumina interfaces is characterised by an adsorption isotherm of a typical L-type, and an adsorption mechanism based on dipolar interaction has been suggested [
Amino sugars represent major constituents of microbial cell walls and hydrolysable soil organic matter. Free amino sugars represent a small part of the dissolved organic C and N pools [
Carbohydrates from soil microbial biomass were reported by Joergensen et al. [
Mineral-organic associations represent a large amount of carbon in terrestrial ecosystems; these associations have a high abundance of microbially derived carbohydrates [
Microaggregates (20–53
Soil type has an impact upon sugar synthesis by microorganisms, reflecting microbial biodiversity and varied ecophysiology between soils. Derrien et al. [
The concentration of carbohydrates generally decreases with soil depth [
Osono et al. [
Rumpel et al. [
Generally, glucose was found in the highest concentrations in the upper humus layer [
A high level of water (in Bg horizon) negatively affects the proportion of amino sugars within the total organic carbon. Enhanced drying of soil decreased the contribution of plant and microbial sugars to soil organic matter in the O and A horizons even though the sugar content of the original plant material increased with drying [
The concentration of soluble sugars in soils from different ecosystems changes over the course of the vegetative season [
Management of ecosystems may affect carbohydrate quantity, quality, and distribution within soils [
Carbohydrates in soil collected from different ecosystems.
Management | Type of extraction | Dominant carbohydrates | Concentrations | Sampling (horizon or depth) | References |
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Rotation of vegetables, legumes, and |
Solution | Glucose, glucuronic, and galacturonic acid | 0.115 |
Ah | [ |
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Arable land (different managements) | Hot water and NaOH extract | Arabinose, xylose, mannose, galactose, glucose, and rhamnose | Up to 358 |
0–10, |
[ |
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Arable land (different rotation, crops, organic and mineral fertilization, biotic treatments, etc.) | Hydrolysate | Xylose, arabinose, galactose, glucose, and mannose, | Up to 4000 |
0–30 cm | [ |
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Forests ( |
Hydrolysate | Xylose, glucose, galactose, arabinose, and mannose | Up to |
Different horizons | [ |
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Grasslands | Hydrolysate | Glucose, galactose, arabinose, mannose, and xylose | More than 700 |
0–75 cm | [ |
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Savannah | Hydrolysate | Glucose, mannose | Up to 2000 |
0–10 cm | [ |
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Shrublands | Hydrolysate | Galactose, glucose, arabinose, and xylose | Up to 2400 |
0–5 cm | [ |
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Prairie | Hydrolysate | Arabinose, galactose, xylose, and glucose | Up to 4000 |
— | [ |
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Four soil types (vegetation not specified) | Hydrolysate | Glucose, galactose, mannose, arabinose, and xylose | Up to 2000 |
0–20 cm | [ |
Manure application, crop rotation, and avoiding tillage for 6 years all increased amino sugar content in soil [
In terms of other treatments, UV-B radiation reduced extractability of carbohydrates from leaf litter of
Change in land use (e.g., pasture to arable land) also causes a new equilibrium for soil carbohydrates, established after 14 and 56 years [
Soil carbohydrate levels have also been reported to decrease during boreal forest succession, root exclusion, grazing of semiarid shrubland, conversion of pasture to cropland, and during conversion of forests on sandy spodosols to
Knowledge of the quantity of vitamins in soils of different ecosystems is poor. Sulochana [
Vitamins may be important in the decontamination of polluted soils and were reported to stimulate PAHs degradation [
Vitamins (riboflavin, vitamin B12, niacin, thiamine, ascorbic and pantothenic acid,
Vitamins in plant root exudates.
Plant | Root exudates | Formula | Reference |
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Riboflavin |
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[ |
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Thiamine |
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[ |
Biotin |
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Pyridoxine |
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L-Ascorbic acid |
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Niacin |
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[ |
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Other plants | Pantothenic acid |
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[ |
Aliphatic, cyclic, and aromatic organic acids play an important role in soil and rhizosphere ecology, as well as in decontamination of polluted sites. Despite much work on the occurrence and behaviour of organic acids in soil, current knowledge is mostly restricted to their L-enantiomers. In future research, determination of the occurrence and role of D-enantiomers of organic acids in soil and rhizodeposition should become a significant focus, particularly relating to their potential in allelopathic interactions, decontamination of polluted sites, and in terms of their roles in plants suitable for phytoremediation purposes. Carbohydrates represent an abundant group within soil organic matter, serving as an indicator of the quality of soil organic matter and of land use changes. Despite the existence of a broad literature on soil carbohydrates and their fractionation within soils across many ecosystems, there still remains a paucity of research on the effects of environmental factors, especially altered soil water content, on qualitative and quantitative changes in soil carbohydrates. Vitamins play an important role in biochemical soil processes and decontamination of polluted sites. More research is needed on their occurrence and behaviour in soil.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This text was created within the framework of the Grants TA02020867, QJ1320040, and the IGA Project 55/2013.