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Abstract

The complexity of humic substances (HS) and their remarkable properties in agricultural applications has attracted and continue to attain the attention of many investigators, bringing over the years new knowledge on their structure, physicochemical and biological properties. Nevertheless, the numerous studies produced controversial results because of the difficulty to identify a precise relationship between the structure and the activity of these substances. Evidences presented here showed that the effects of HS on plant growth depends on the source, concentration and molecular weight of humic fractions and mainly on different chemical compounds contained into them. Humic matter appears also to display a hormone-like activity in particular an auxin like activity. It is not clear if this activity is strictly linked to the chemical structure of HS or whether it depends on hormones of microbial origin such as indole acetic acid entrapped into them. In any case, HS exhibit stimulatory effects on plant cell growth and development. In this review, the relationship between humic substance structure, chemical composition and physiological effects on plant growth and metabolism are examined. In particular, the responses of plants to humic substances are described, as well as the regulatory circuits that allow plants to cope with humus. Furthermore, how the present findings can add new information to the humic substances issue is widely discussed.

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... Humic acids, known as plant growth stimulants, are a class of macromolecular substances widely found in the natural environment, formed by plant and animal residues through complex biochemical processes, with complex structures and a variety of active functional groups, and thus have a strong ion exchange and adsorption ability [19]. Many studies have demonstrated that humic acid affects root growth and nutrient uptake in roots [19][20][21][22] and modulates plant growth and development via the auxin pathway [23]. ...
... Humic acids, known as plant growth stimulants, are a class of macromolecular substances widely found in the natural environment, formed by plant and animal residues through complex biochemical processes, with complex structures and a variety of active functional groups, and thus have a strong ion exchange and adsorption ability [19]. Many studies have demonstrated that humic acid affects root growth and nutrient uptake in roots [19][20][21][22] and modulates plant growth and development via the auxin pathway [23]. Humic acids improve stress tolerance in plants by reducing reactive oxygen species (ROS) overaccumulation and malondialdehyde (MDA) contents, thereby reducing plasma membrane permeability [19,21]. ...
... Many studies have demonstrated that humic acid affects root growth and nutrient uptake in roots [19][20][21][22] and modulates plant growth and development via the auxin pathway [23]. Humic acids improve stress tolerance in plants by reducing reactive oxygen species (ROS) overaccumulation and malondialdehyde (MDA) contents, thereby reducing plasma membrane permeability [19,21]. Supplementation with humic acids increased chlorophyll contents and improved thylakoid structure, thus promoting photosynthetic efficiency [20]. ...
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Zucchini (Cucurbita pepo L.) is one of the main vegetable crops grown under protected cultivation in northern China. Low-temperature (LT) stress severely inhibits the growth of zucchini seedlings, resulting in reductions in yield and quality. Here, using three kinds of different humic acids, including coal-based humic acid (CHA), fulvic acid (FA), and biochemical humic acid (BHA), we investigated the effects of humic acids against LT stress (5°C) in zucchini seedlings. Treatment with all three kinds of humic acids improves LT stress tolerance by decreasing oxidative damage through increases in antioxidative enzyme activities and the contents of soluble sugar and proline in zucchini seedlings, especially after BHA application. Comparative transcriptomic analysis revealed that a total of 17 differentially expressed genes (DEGs) were commonly induced in the leaves of FA-, CHA-, and BHA-treated zucchini seedlings under LT stress, including calmodulin, ethylene-responsive transcription factors (TFs), peroxidases, and 10 TFs, including two NAC and seven WRKY genes. Altogether, these results indicated that supplementation with humic acids reprograms plant metabolism and modulates the expression of genes involved in ROS scavenging, phytohormone metabolism, or signaling pathways, finally improving LT stress tolerance in zucchini seedlings.
... Información Tecnológica -Vol. 29 Nº 5 -2018 resistentes a la degradación biológica , por lo que reciben la denominación de materia orgánica estabilizada (Nebbioso y Piccolo, 2011;Muscolo et al., 2013). ...
... Químicamente, las SH son agrupaciones supramoleculares complejas originadas en largos procesos de descomposición y repolimerización de los restos orgánicos. Las unidades fundamentales de su macroestructura son compuestos aromáticos de carácter fenólico, unidos por cadenas alifáticas de diferentes tamaños, exhibiendo diferentes grupos funcionales y con cierto contenido de compuestos nitrogenados, tanto cíclicos como alifáticos, sintetizados por ciertos microorganismos del suelo (Piccolo & Mbagu, 1999;Muscolo et al., 2013). Las SH exhiben naturaleza coloidal y propiedades ácidas, a menudo se encuentran en el suelo asociadas mediante puentes de hidrógeno y fuerzas de Van der Walls a otras fracciones de composición química definida como aminoácidos, azúcares, polisacáridos y proteínas, o a las arcillas, formando complejos arcillo-húmicos, en los cuales radica un sinnúmero de funciones importantes para el suelo (Piccolo, 1996;Theng, 2012). ...
... Las SH exhiben naturaleza coloidal y propiedades ácidas, a menudo se encuentran en el suelo asociadas mediante puentes de hidrógeno y fuerzas de Van der Walls a otras fracciones de composición química definida como aminoácidos, azúcares, polisacáridos y proteínas, o a las arcillas, formando complejos arcillo-húmicos, en los cuales radica un sinnúmero de funciones importantes para el suelo (Piccolo, 1996;Theng, 2012). En la actualidad se tienen aproximaciones diferentes a la composición elemental y a la estructura de las SH (Spaccini y Piccolo, 2009); sin embargo, su estudio se dificulta en gran medida por la complejidad intrínseca dado principalmente por la heterogeneidad de procesos y condiciones en las que se originan, debido a esto se ha alcanzado un alto grado de desarrollo en las técnicas utilizadas para su caracterización (Nebbioso y Piccolo, 2011;Muscolo et al., 2013;Drosos et al., 2017). Debido a su dinámica y gran complejidad la MOH podría también denominarse como un "estado de la materia orgánica del suelo". ...
... On this account, the use of bio-fertilizers in agricultural practices is proposed as a safe tool to enhance the nutritional properties of food crops. Bio-fertilizers are recognized as environment-friendly compounds with beneficial effects on plants 8,9 . In particular, they decrease the use of chemical fertilizers by increasing the amount of micro-and macro-nutrients taken up by plants, positively influencing root morphology and plant growth 10,11 . ...
... www.nature.com/scientificreports/ Recent studies suggest that active molecules contained in bio-fertilizers can promote nitrogen assimilation [8][9][10][11][12] . Furthermore, the induction of the metabolic pathway associated with the synthesis of phenylpropanoids in plants treated with bio-fertilizers may explain why these products can help plants to overcome stress situations 15,16 . ...
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The long-term application of chemical fertilizers has caused to the farmland soil compaction, water pollution, and reduced the quality of vegetable to some extent. So, its become a trend in agriculture to find new bio-fertilizers. Chlorella extract is rich in amino acids, peptides, nucleic acids, growth hormones, potassium, calcium, magnesium, iron, zinc ions, vitamin E, B1, B2, C, B6, folic acid, free biotin and chlorophyll. Chlorella extract can promote biological growth, mainly by stimulating the speed of cell division, thereby accelerating the proliferation rate of cells and playing a role in promoting plant growth. Whether Chlorella extract can be used to improve the growth of pepper (Capsicum annuum), needs to be verified. In current study, a pepper variety 'Chao Tian Jiao' was used as experiment material, by determining the changes of the related characteristics after spraying the seedlings with Chlorella extract, and its effect on growth of Capsicum annuum plants was investigated. The results showed that the Chlorella extract significantly increased plant height of pepper seedlings (treatment: 32.2 ± 0.3 cm; control: 24.2 ± 0.2 cm), stem diameter (treatment: 0.57 ± 0.02 cm; control: 0.41 ± 0.03 cm) and leaf area (treatment: 189.6 ± 3.2 cm²; control: 145.8 ± 2.5 cm²). Particularly, the pepper seedlings treated with Chlorella extract, developed the root system in better way, significantly increased the chlorophyll a, and the activities of SOD, POD and CAT enzymes were also improved significantly. Based on our results, we can speculate that it is possible to improve the growth of Capsicum annuum seedlings and reduce the application of chemical fertilizers in pepper production by using Chlorella extract.
... The effects of HS on plants depend on the materials that are formed; the concentrations of fulvic and humic acids; the doses used for each cultivar and the type of soil. The HS are composed of several functional groups that directly or indirectly affect the physical and chemical attributes of the soil (NEILSEN et al., 2004). ...
... Conversely, there is no consensus on the mechanisms of action of these organic acids on plants. Although different plant responses to concentration, molecular weight, organic acid structure and HS sources are known (MUSCOLO et al., 2013), discussing the effects at a physiological level is often complicated or even inconclusive, especially under uncontrolled conditions, such as those normally found in field experimentation; so there is a shortage of works on this topic (ZANDONADI et al., 2013). ...
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The complexity of humic substances (HS) and their properties in agricultural applications have attracted the attention of many researchers. However, controversial results have been obtained, because of the difficulty in identifying a precise relationship between the structure and activity of these substances. This study aimed to evaluate the influence of different frequencies and concentrations of humic substances on the behavior of physical, chemical and microbiological soil attributes. The experiment was carried out at Embrapa Cassava and Fruticulture in Latossolo Amarelo Distrocoeso [(Xanthic Ferralsol (Densic); Oxisol], with a completely randomized block design with four repetitions in a split-plot scheme, with three application frequencies (F1 = 15 days, F2 = 30 days and F3 = 45 days) and four concentrations of humic substances (C1 = 0 ml.L-1, C2 = 3 ml.L-1, C3 = 6 ml.L-1 and C4 = 9 ml.L-1). The humic substance applied at a frequency of 45 days positively favored the physical and chemical attributes of the soil, mainly at concentrations of 6 and 9 ml.L-1, due to the increase in microporosity. This information can be used to improve the performance of agricultural practices, especially those related to soil preparation, use of agricultural inputs, water management, soil water content and, especially, soil management practices.
... Humic acid is composed of a complex supramolecular association known as humic substances (HSs), which is produced by humification of organic matter such as peat, compost, and plants in soil environments [1]. Although HSs are amorphous and depend on their source of extraction from soil, partial polymeric structures can be identified containing diverse aromatic and aliphatic structures [2,3]. These physicochemical properties have not only prompted their agricultural use as soil amendments, but also as plant growth stimulators [3][4][5]. ...
... Although HSs are amorphous and depend on their source of extraction from soil, partial polymeric structures can be identified containing diverse aromatic and aliphatic structures [2,3]. These physicochemical properties have not only prompted their agricultural use as soil amendments, but also as plant growth stimulators [3][4][5]. There is evidence that wheat seedlings directly take up and accumulate HA in tissues [6], suggesting that HA stimulates diverse transcriptional changes promoting the physiological and developmental processes of plants. ...
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Humic acid (HA) is a principal component of humic substances, which make up the complex organic matter that broadly exists in soil environments. HA promotes plant development as well as stress tolerance, however the precise molecular mechanism for these is little known. Here we conducted transcriptome analysis to elucidate the molecular mechanisms by which HA enhances salt stress tolerance. Gene Ontology Enrichment Analysis pointed to the involvement of diverse abiotic stress-related genes encoding HEAT-SHOCK PROTEINs and redox proteins, which were up-regulated by HA regardless of salt stress. Genes related to biotic stress and secondary metabolic process were mainly down-regulated by HA. In addition, HA up-regulated genes encoding transcription factors (TFs) involved in plant development as well as abiotic stress tolerance, and down-regulated TF genes involved in secondary metabolic processes. Our transcriptome information provided here provides molecular evidences and improves our understanding of how HA confers tolerance to salinity stress in plants.
... Our results are consistent with Elmongy et al. (2018), who reported that applying HA at high concentrations inhibited roots growth. Many researchers proved that HA exerts its influence by improving plant nutrition or hormone-like activity (Nardi et al. 2009;Trevisan et al. 2010;Muscolo et al. 2013). ...
... We have observed that HA and ZnO-NPS have a promotional effect on rooting of date palm shoots. HA had IAA-like activity (Muscolo et al. 2013). HA plays a vital role in manufacturing auxins and cytokinins and preserves endogenous natural hormones in plant tissues (Elmongy et al. 2018). ...
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Date palm (Phoenix dactylifera L.) micropropagation still faces many problems, such as reduced growth and development of callus, low multiplication efficiency and low rooting rate. The effect of Humic Acid (HA; 0, 0.5, 2.5, and 5.0 mg L−1) and Zinc oxide nanoparticles (ZnONPs; 0, 50, 75 and 150 mg L−1) at different stages of micropropagation (i.e., callus establishment, shoot multiplication and rooting) was studied in date palm cv. Quntar. Media supplemented with 2.5 mg L−1 HA in combination with 50 m L−1 ZnO-NPs gave the highest callus induction (274 mg/jar), the highest percentage of callus producing buds (83.34%), and average bud formation (14.2) per callus. The macronutrients Nitrogen (N), Phosphorus (P), Potassium (K), Sulfur (S) as well the micronutrient Zinc (Zn), significantly increased in in vitro shoots regenerated in medium containing of 2.5 mg L−1 HA and 50 mg L−1 ZnO-NPs compared to other treatments. The addition of HA and ZnO-NPs to the medium was most effective in root regeneration and the number of roots per shoot, where the best result (83.34%, 4.4 roots per shoot, respectively) was obtained using 2.5 mg L−1 humic acid and 75 mg of L−1 zinc oxide (ZnO-NPs), compared with other treatments. These results also indicate that using 2.5 mg L−1 HA combined with 75 m L−1 ZnO-NPs as a supplement can increase antioxidant enzymes CAT and POD compared with other treatments. The data revealed that maximum chlorophyll content of shoots occurred in a medium supplemented with 2.5 mg L−1 HA and 75 mg L−1 ZnO-NPs. Furthermore, we found that the combined application between 2.5 mg L−1 HA + 75 mg L−1 ZnO-NPS resulted in the highest shoots content of endogenous IAA (3.644 µg.kg−1), compared with other treatments.
... HS have the capacity of coordinating physical, chemical, and biological soil properties through the regulation of ions mobilization and transports in the environment, with important consequence in the rhizosphere interactions [6]. Soil fertility is dependent on the amount and characteristic of HS that with their physical-chemical and biochemical properties are able to promote plant growth and metabolism [7][8][9][10][11][12], influencing remarkably the crop efficiency. Rose et al. [13] showed, by a random-effects meta-analysis, that plants treated with HS have a significant increment (22%) in root and shoot dry weight. ...
... Callus grown with humic substance always increased its weight compared to control [29]. In presence of soil water soluble phenolic fraction, callus biomass was comparable to control [7]; relative growth rate where higher in the early stage of growth (15 days) for HS treated callus and hormones compared to control and SWSP treated ones; all the calluses appeared white and in good health. Table 2. Biomass (g) of Pinus laricio callus after 28 d of subculture in presence of hormones or humic substances (HSs) or soil water soluble phenolic fraction (SWSP) at 1.0 mg C L −1 . ...
Article
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Significant benefit of soil organic matter (SOM) to crop productivity is scientifically well documented. The main constituents and active fractions of SOM are humic substances (HS) and phenolic compounds. Since both these two components strongly impact plant–soil relationship, it is importantly from an ecological point of view to discriminate their biological effects and relating them to their composition. In this study we compared the biological effects of HS, and the soil water soluble phenols (SWSP) on growth, antioxidant activities, carbohydrates, proteins, phenols, and vitamins of Pinus laricio callus. Each extract was assessed for the content of low molecular weight organic acids, soluble carbohydrates, fatty acids, and phenolic acids. Moreover, Fourier transform infrared (FT-IR) and surface-enhanced Raman scattering (SERS) spectroscopies were applied to study their molecular structure. The results showed that HS produced better callus growth compared to the control and SWSP. Carbohydrates decreased in presence of HS while proteins, vitamin C and E increased. In contrast, in callus treated with SWSP the amount of glucose and fructose increased as well as all the antioxidant activities. The data evidenced that HS rich in tartaric and fatty acids had beneficial effects on callus growth contrary to soil water-soluble phenols rich in aldehydes, and syringic, ferulic, and benzoic acids.
... Nevertheless, the origin, the formation and the structure of HLS are a matter of controversial scientific debate over two centuries. This domain is still of a great interest pushed by the recognized importance of humic substances for understanding the fertility of natural soils but also due to its remarkable applications on agriculture or horticulture as soil conditioners and biostimulants (Muscolo et al., 2013). ...
... Thus FLA are usually more associated with the biostimulation of plant/root growth than HLA. However, this trend might vary depending on HLS structure and concentration (Muscolo et al., 2013). For the biostimulation of plant growth, different results have been reported in the scientific literature. ...
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In France, digestates from anaerobic digestion plants have to pass through homologation process or reach certain specific standards to be commercialized. In this study, valorisation processes regarding the production of added-value products from urban digestates are being explored. Humic Acids (HA) extracted from upcycled organic products such as composts have been demonstrated to improve soil fertility [1] and industrial applications have been proven more recently [2]. However, very few studies addressed HA-recovery from digestates [3]. Preliminary tests presented in this study were carried out in order to assess the feasibility of recovering HA from such urban digestates. The samples were a Food Waste/Cardboard digestate (FW/CB-D) from a pilot reactor and an Organic Fraction of Municipal Solid Waste digestate (OFMSW-D) from a full-scale plant. HA-extraction was tested on raw digestates and on its solid fractions after laboratory centrifugation. A practical approach for HA extraction was performed, adapted from [4]: NaOH 0.1 M was added until pH 12 was reached. The solution was stirred for 24h. After the alkaline extraction was performed, the digestate was centrifuged. The supernatant was filtered at 0.45 μm and acidified at different pH (1, 2, 3, 5 and 7). This solution was centrifuged to isolate the insoluble fraction containing HA. The recovered HA were redissolved for Fluorescence 3D analysis. Another acidification at pH 3 was performed where the precipitate was washed several times with distilled water and freeze-dried for Mid-Infrared analysis and calculation of recovering yields. Recovered HA were compared to HA isolated from a leonardite commercial solution and to references from the International Humic Substances Society (IHSS). Freeze-dried HA yields were low: from 3 to 4% (volatile solids:volatile solids) and 1 to 2%, for raw mass of FW/CB-D and OFMSW-D respectively. HA extracted from FW/CBD were observed to be similar to a river sediment reference from the International Humic Substances Society. The HA from OFMSW was closer to the HA isolated from the leonardite solution, but it presented more proteins in the 3D fluorescence spectra. When HAs were extracted from the solid fraction of digestates, HA extraction yields and spectra were almost unchanged. The pH for acidification played an important role in HA isolation. pH 1, 2 and 3 were observed to perform similarly (quality and quantity) but pH 5 and 7 resulted in less extraction of HA and poorer quality. Industrial feasibility of HA-like extraction from digestate would rely on extraction yields, product quality and residual matter management options. Experiments will be carried out in order to further evaluate the quality of the products regarding biodegradability and impact on root growth
... The origins and distributions of tOM in the Canada Basin in the western Arctic Ocean have been extensively studied, making it a useful system for investigating interactions between tOM and ocean microbiomes. In spring and summer, humic-rich OM is transported by riverine inputs to the surface mixed layer of the Arctic Ocean shelves [19,20]. In shelf waters, tOM is partially photodegraded [21], while some flocculates upon mixing with salt water and sinks to the sediments along with particulate OM [15]. ...
Article
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Background The Arctic Ocean receives massive freshwater input and a correspondingly large amount of humic-rich organic matter of terrestrial origin. Global warming, permafrost melt, and a changing hydrological cycle will contribute to an intensification of terrestrial organic matter release to the Arctic Ocean. Although considered recalcitrant to degradation due to complex aromatic structures, humic substances can serve as substrate for microbial growth in terrestrial environments. However, the capacity of marine microbiomes to process aromatic-rich humic substances, and how this processing may contribute to carbon and nutrient cycling in a changing Arctic Ocean, is relatively unexplored. Here, we used a combination of metagenomics and metatranscriptomics to assess the prevalence and diversity of metabolic pathways and bacterial taxa involved in aromatic compound degradation in the salinity-stratified summer waters of the Canada Basin in the western Arctic Ocean. Results Community-scale meta-omics profiling revealed that 22 complete pathways for processing aromatic compounds were present and expressed in the Canada Basin, including those for aromatic ring fission and upstream funneling pathways to access diverse aromatic compounds of terrestrial origin. A phylogenetically diverse set of functional marker genes and transcripts were associated with fluorescent dissolved organic matter, a component of which is of terrestrial origin. Pathways were common throughout global ocean microbiomes but were more abundant in the Canada Basin. Genome-resolved analyses identified 12 clades of Alphaproteobacteria , including Rhodospirillales , as central contributors to aromatic compound processing. These genomes were mostly restricted in their biogeographical distribution to the Arctic Ocean and were enriched in aromatic compound processing genes compared to their closest relatives from other oceans. Conclusion Overall, the detection of a phylogenetically diverse set of genes and transcripts implicated in aromatic compound processing supports the view that Arctic Ocean microbiomes have the capacity to metabolize humic substances of terrestrial origin. In addition, the demonstration that bacterial genomes replete with aromatic compound degradation genes exhibit a limited distribution outside of the Arctic Ocean suggests that processing humic substances is an adaptive trait of the Arctic Ocean microbiome. Future increases in terrestrial organic matter input to the Arctic Ocean may increase the prominence of aromatic compound processing bacteria and their contribution to Arctic carbon and nutrient cycles.
... However, there is still disagreement about the origin of these substances. Muscolo et al. (2013) suggested that they are produced by biochemical reactions in the transformation of biological debris; different conditions of vegetation, climate, soil type, and biological activity generate differences in its components: humic acids (HA), fulvic acids (FA) and humins (Watson et al. 2000). Regarding these components, HAs are indicators of SOM quality and contribute to the long-term storage of C in soils and hence, to the mitigation of greenhouse gas emissions (Piccolo 1996). ...
Article
Soil organic carbon (SOC) is the main element in soil organic matter (SOM) and its storage or release into the atmosphere is sensitive to changes in land use. This study evaluated SOC storage and SOM quality in the Metropolitan Regional Natural Park, Cerro El Volador, MedelIín-Colombia, in areas where plant cover was restored with plants from different functional groups consisting of secondary vegetation (SV), forest plantations of Eucalyptus globulus Labill. (EUC) and Pinus patula Schltdl. & Cham. (PIN), and pastures (PAS). Soil samples were taken at the O horizon and at two soil depths at the A horizon (0–10 and 10–20 cm). The quality of the SOM was evaluated through humification indices, spectrophotometric tests and carbon distribution in humic substances. The highest storage of SOC in the O horizon occurred in PIN, followed by EUC, SV and PAS. In descending order, the vegetation with the highest SOC values for the A horizon at both depths evaluated were EUC, PAS, PIN and SV. Humification indices showed that the SOM was mainly composed of fresh SOM with little humification. The humification process of SOM evolved towards humic acids of the P-group. These results show that the change of cover significantly affects the storage of SOC, the characteristics of SOM and the properties of the soil.
... Humic substances (HS) are organic compounds formed from plant or animal residues present in soils, which are degraded in a process known as humification resulting from the activity of microorganisms such as fungi and bacteria [28]. These substances represent approximately 25% of the total organic carbon present on the planet [29]. ...
Article
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The objective of this review is to present a compilation of the application of various biostimulants in strawberry plants. Strawberry cultivation is of great importance worldwide, and there is currently no review on this topic in the literature. Plant biostimulation consists of using or applying physical, chemical, or biological stimuli that trigger a response-called induction or elicitation with a positive effect on crop growth, development, and quality. Biostimulation provides tolerance to biotic and abiotic stress, and more absorption and accumulation of nutrients, favoring the metabolism of the plants. The strawberry is a highly appreciated fruit for its high organoleptic and nutraceutical qualities since it is rich in phenolic compounds, vitamins, and minerals, in addition to being a product with high commercial value. This review aims to present an overview of the information on using different biostimulation techniques in strawberries. The information obtained from publications from 2000-2022 is organized according to the biostimulant's physical, chemical, or biological nature. The biochemical or physiological impact on plant productivity, yield, fruit quality, and postharvest life is described for each class of biostimulant. Information gaps are also pointed out, highlighting the topics in which more significant research effort is necessary.
... Fermentation of these substances occurs via activity of soil microbiota under selected physio-molecular conditions such as controlled temperature, time, water, and aeration (Canellas and Olivares, 2014). Regardless of the source of origin of the carbon (i.e., C3 and C4), HS and humic acids extracted from the soil are structurally similar (Muscolo et al., 2013;García et al., 2016a). However, HS have wide and extensive functions in plants Canellas and Olivares, 2014). ...
Article
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Humic substances (HSs) have considerable effects on soil fertility and crop productivity owing to their unique physiochemical and biochemical properties, and play a vital role in establishing biotic and abiotic interactions within the plant rhizosphere. A comprehensive understanding of the mode of action and tissue distribution of HS is, however, required, as this knowledge could be useful for devising advanced rhizospheric management practices. These substances trigger various molecular processes in plant cells, and can strengthen the plant's tolerance to various kinds of abiotic stresses. HS manifest their effects in cells through genetic, post-transcriptional, and post-translational modifications of signaling entities that trigger different molecular, biochemical, and physiological processes. Understanding of such fundamental mechanisms will provide a better perspective for defining the cues and signaling crosstalk of HS that mediate various metabolic and hormonal networks operating in plant systems. Various regulatory activities and distribution strategies of HS have been discussed in this review.
... The effect of HS in improving nutrient assimilation and plant metabolism is well recognized. Previous studies indicated that humic fraction increases cell growth, metabolism, and nitrate uptake [88,89]. [90] has reported that root architecture and nutrients uptake are directed affected by humus, enhancing plant yield. ...
Chapter
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In strongly weathered tropical soils, humus and humic substances (HSs) appear to play an important role in soil fertility because they represent the dominant reservoir and source of plant nutrients. As the refractory organic carbon form of soil, HSs play a vital role in the atmospheric CO 2 sequestration. Detailed classification of humus forms in tropical ecosystems and the dynamics and function of humus are still poorly understood. Nevertheless, in tropical environment many studies indicated that it is very difficult to differentiate between tropical humus, at least in normally drained soil. Moders, mulls, and Amphimull are the dominant humus forms in the topsoil of tropical environment. Knowing the mechanisms of formation, the dynamics and the methods of characterization of humus in tropical zones are a scientific challenge. This chapter aims to share recent findings from a broad humus in tropical soil and research related to this theme.
... Even today, there is no consensus on which modes of action of humic substances in plants. Some authors propose that the action of HS is related to the dissociation of the humic superstructure and subsequent availability of bioactive fractions and humic fragments that mimic phytohormones, thus promoting the regulation of hormone signaling pathways through the interaction of these molecules with the plant root system (Dobbss et al. 2010;Mora et al. 2012;Muscolo et al. 2013;Olaetxea et al. 2019;de Hita et al. 2020). However, it has been shown that the "fouling stress" resulting from the accumulation of humic acids in the roots, which causes pore fouling and affects plant transpiration and root electrical conductivity, is responsible for metabolic changes and the regulation of ROS concentrations and the activity of antioxidative enzymes (Asli and Neumann 2010;García et al. 2014;Aguiar et al. 2016). ...
Article
Agriculture is responsible for consuming the largest amount of water in the world. Water availability is the environmental factor that most limits the sustainability of agricultural systems. The adoption of sustainable technologies that improve plant water use efficiency has become increasingly important in modern agriculture. Humic acids (HA) acts as a rhizospheric bioeffector, stimulating the biochemical and physiological activities of plants. The objective of this study was to evaluate the potential of humic acids from vermicompost (HAVC), previously characterized by ATR-FTIR and 1 H-NMR, in stimulating the emission kinetics of the transient fluorescence of chlorophyll a, the concentrations of photosynthetic pigments and soluble metabolites, development of the root system and accumulation of fresh and dry biomass in rice (Oryza sativa L.) under normal growth conditions and water deficit. The experimental design was completely randomized, with four treatments (Control; HAVC; PEG-6000; HAVC + PEG-6000). The application of HAVC in plants under water deficit was efficient in maintaining photosynthesis, with an effect as an eustressor. HAVC triggered the increase of plant biomass and root development of plants under water deficit. HAVC acted on osmotic regulation and the influx and remobilization of different forms of nitrogen, enhancing protection against stress. HAVC in the rhizosphere induced plants with higher root biomass, partially due to better photosynthetic performance.
... Crop rotation can also result in a better control of some soil-borne diseases, such as in potatoes affected by Rhizoctonia solani and Streptomyces scabies [26]. In addition, the application of plant growth-promoting rhizobacteria (PGPR), biofertilisers, composts, mycorrhiza, biochars, and humic and fulvic acids can augment nutrient acquisition and assimilation, improve soil texture and plant growth, and induce systemic resistance to biotic and abiotic stresses [26][27][28][29][30][31][32]. For example, the distribution to the soil of a biofertiliser that contained a mixed fungal and bacterial microflora induced conferred protection against Fusarium wilt of banana caused by Fusarium oxysporum f. sp. ...
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To reduce the impact of chemical pesticides on the environment, there are relevant efforts to enhance the possibility of controlling plant diseases using environmentally friendly biocontrol agents or natural products that show pathogen control capacity. The European Union, FAO, and the United Nations largely promote and finance projects and programs in order to introduce crop protection principles that can attain sustainable agriculture. Preventive measures related to the choice of cultivars, soil fertility, integrated pest management (IPM), and organic farming strategies are still the basis for obtaining satisfactory crop yields and reducing classical pesticide utilisation through the application of commercially available and ecofriendly control agents. Effective pathogen detection at borders to avoid quarantine pathogens is mandatory to reduce the risk of future epidemics. New technical support for the development of sustainable pathogen control is currently being provided by forecasting models, precision farming, nanotechnology, and endotherapy. New biocontrol agents and natural products, disease management through plant nutrition, systemic resistance inducers, and gene-silencing technology will provide solutions for obtaining satisfactory disease control in horticulture. The "multi-stakeholder partnership" strategy can promote the implementation of sustainable crop protection.
... For example, hormone-like and catalytic activities of HS directly stimulate shooting and rooting of plants [117]. Moreover, some studies suggest that HS may directly stimulate activity of H+-ATPase and ion transporters in the root plasma membrane, consequently enhancing nutrient acquisition [101,118]. ...
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Humic substances (HS), as important environmental components, are essential to soil health and agricultural sustainability. The usage of low-rank coal (LRC) for energy generation has declined considerably due to the growing popularity of renewable energy sources and gas. However, their potential as soil amendment aimed to maintain soil quality and productivity deserves more recognition. LRC, a highly heterogeneous material in nature, contains large quantities of HS and may effectively help to restore the physicochemical, biological, and ecological functionality of soil. Multiple emerging studies support the view that LRC and its derivatives can positively impact the soil microclimate, nutrient status, and organic matter turnover. Moreover, the phytotoxic effects of some pollutants can be reduced by subsequent LRC application. Broad geographical availability, relatively low cost, and good technical applicability of LRC offer the advantage of easy fulfilling soil amendment and conditioner requirements worldwide. This review analyzes and emphasizes the potential of LRC and its numerous forms/combinations for soil amelioration and crop production. A great benefit would be a systematic investment strategy implicating safe utilization and long-term application of LRC for sustainable agricultural production.
... Humic acid is a product of the biodegradation of plant parts and microbes and has direct effects on plant growth and metabolism. Its growth promotive effects are reported in many crops, which cannot be attributed solely to hormone-like activity [93]. Humic acid is also found to minimize oxidative stress in plants. ...
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Global food security for a growing population with finite resources is often challenged by multiple, simultaneously occurring on-farm abiotic stresses (i.e., drought, salinity, low and high temperature, waterlogging, metal toxicity, etc.) due to climatic uncertainties and variability. Breeding for multiple stress tolerance is a long-term solution, though developing multiple-stress-tolerant crop varieties is still a challenge. Generation of reactive oxygen species in plant cells is a common response under diverse multiple abiotic stresses which play dual role of signaling molecules or damaging agents depending on concentration. Thus, a delicate balance of reactive oxygen species generation under stress may improve crop health, which depends on the natural antioxidant defense system of the plants. Biostimulants represent a promising type of environment-friendly formulation based on natural products that are frequently used exogenously to enhance abiotic stress tolerance. In this review, we illustrate the potential of diverse biostimulants on the activity of the antioxidant defense system of major crop plants under stress conditions and their other roles in the management of abiotic stresses. Biostimulants have the potential to overcome oxidative stress, though their wider applicability is tightly regulated by dose, crop growth stage, variety and type of biostimulants. However, these limitations can be overcome with the understanding of biostimulants’ interaction with ROS signaling and the antioxidant defense system of the plants.
... Moreover, the alteration of substrate-plant-microbiota interactions affects the number of chemical compounds in plant cells such as those associated with C-N-P cycles and photosynthesis, thus determining important biochemical changes to primary and secondary metabolisms [22,23]. HLSs may significantly affect many plant physiological processes through the increase of cation exchange and water retention capacities, the modification of the absorption kinetics and ion transportation, and chlorophyll and nucleic acids biosynthesis [24][25][26]. Recently, an increasing interest of growers and industries towards HLSs have been recorded, because of their multiple positive outcomes on plant growth and quality. ...
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Humic-like substances (HLS) are among the most used biostimulants in agriculture as a means for improving plant growth, nutrient uptake, crop yield, and stress tolerance. HLS derived from municipal biowastes were applied as a substrate drench in order to evaluate their biostimu-latory effect on the growth and ornamental quality of Orange Jasmine (Murraya paniculata [L.] Jacq.) potted plants. Two HLS, derived from the digestion of the organic humic fraction and from com-posting of a mix of sewage sludge digestate and gardening residues, were compared with a commercial leonardite-based product in the framework of a greenhouse experiment in soilless culture. The application of the two biowaste-derived HLS resulted in plants showing a 39.9%, 87.0%, 111.6%, 35.4%, 37.9%, 35.3%, and 81.3% increase in plant height, number of flowers and fruits, leaf production, total dry biomass, root length, and water use efficiency, respectively, compared to those treated with the commercial product and the untreated (control) plants. The enhanced growth performance of HLS-treated plants was due to the higher chlorophyll relative content (+24.2% on average) and net photosynthesis (+114.7% on average) of their leaves. The positive results obtained from the application of non-commercial HLS suggest that biowaste recycling is a sustainable and environment-friendly source of biostimulants, as an alternative to agrochemicals and existing leonardite-based plant biostimulants.
... Nevertheless, as Muscolo and collaborators [10] explained in their 2014 article, HSs are now recognized as the structural association of mixtures of small and distinct organic molecules, which are linked together via hydrogen bonds and hydrophobic interactions, and that their diversity is due to different external perturbations and resource usage strategies employed by the ecosystems. This definition suggests that, rather than the molecular constituents, it is molecular structure and size that seem to be critical in plant-HS interaction. ...
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Climate change is a pressing matter of anthropogenic nature to which agriculture contributes by abusing production inputs such as inorganic fertilizers and fertigation water, thus degrading land and water sources. Moreover, as the increase in the demand of food in 2050 is estimated to be 25 to 70% more than what is currently produced today, a sustainable intensification of agriculture is needed. Biostimulant substances are products that the EU states work by promoting growth, resistance to plant abiotic stress, and increasing produce quality, and may be a valid strategy to enhance sustainable agricultural practice. Presented in this review is a comprehensive look at the scientific literature regarding the widely used and EU-sanctioned biostimulant substances categories of silicon, seaweed extracts, protein hydrolysates, and humic substances. Starting from their origin, the modulation of plants’ hormonal networks, physiology, and stress defense systems, their in vivo effects are discussed on some of the most prominent vegetable species of the popular plant groupings of cucurbits, leafy greens, and nightshades. The review concludes by identifying several research areas relevant to biostimulant substances to exploit and enhance the biostimulant action of these substances and signaling molecules in horticulture.
... Most prominent biostimulant is humic acid (HA), which has direct and indirect effects on morpho-physiological growth of plants (Peña-Méndez et al., 2005). HA is mainly derived from humic substances and finally decomposed material contains 60% of organic matter in soil (Muscolo et al., 2013). On other hands, HA application to the soil not only improves the various soil properties (such as structure stability, biological activity and effecting soil PH), but also results in better roots development, improve water holding capacity, carbon sequestration, cation exchange capacity, and upgrade the availability of nutrients from rhizosphere (Gümüş and Şeker, 2015). ...
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The experiment was conducted to optimize the level of humic acid, zinc and boron for better growth, enhanced yield and grain quality of wheat crop cultivated under field condition. Growth characteristics, yield and its components, and zinc concentrations in straw and grain were analyzed under two application rate of humic acid (0 and 10 kg ha-1), three level of boron (B0 = 0, B1 = 2 and B2 = 4 kg ha-1) and zinc (Zn0 = 0, Zn1 = 5 and Zn2 =10 kg ha-1). Results revealed that application of Zn at 10 kg ha-1 and B at 4 kg ha-1 combine with humic acid (10 kg ha-1) significantly increased yield and its components (except flag leaf area under humic acid application), and Zn contents in straw. The maximum plant height, spike length and grain filling rate were recorded at Zn2 and B2 with humic acid application. Maximum grain yield was produced for Zn2 and B2 under humic acid application, which was associated with higher 1000-grain weight and biological yield. Maximum biological and straw yields were produced by application of Zn2 and B2 under humic acid fertilization. Maximum Zn contents in straw have been recorded for Zn2 and B2 under humic acid application, while maximum values of crude protein and Zn contents in Zn2 and B2 were statically same with Zn1 and B1 under humic acid application. Furthermore, the highest boron contents in grain were recorded for Zn2 and B2, and these values were statistically same with Zn2 and B1 under humic acid application. It is concluded that application of Zn2 and B2 in combination with humic acid could be a good agronomic practice to enhance the zinc content in straw and grain yield of wheat crop.
... On the other hand, plant bio-stimulants usage as a protection agency to modify plant productivity and crop growth vigor. Plant bio-stimulants are well-known as friendly environment-compounds with beneficial effects on various crops [9,10]. Bio-stimulants include different substances and micro-organisms that stimulate plant growth [11]. ...
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There are more studies about plant bio-stimulants but no clear results about which is the best one in improving vegetable crops specially cucumber. The aim of this study is to screen the effect of various bio-stimulants in improving cucumber (Cucumis sativus L.) growth under soilless culture via root application by modifying coco-peat culture media substrate. In the present study, we tested fifteen treatments as follow: T1-control (CK); T2-10 mM putrescine (Put); T3-250 ppm seaweed (Sea); T4-0.02 ppm meta-topolin (MT); T5-100 ppm naphthalene acetic acid (NAA); T6-400 ppm polyaspartic acid (PAS); T7-50 ppm sodium nitrophenolate (98% NIT); T8-100 ppm tryptophan (AAF); T9-1% fulvic acid (FUL); T10-10 7 CFU/ml Bacillus subtilis (BAS); T11-10 6 CFU/ml Trichoderma (TRI); T12-50 ppm alanine (ALa); T13-150 ppm salicylic acid (SA); T14-1 mM silicon (SiO 2) and T15-0.001 ppm 24-epibrassinolide (EBR). The results obviously showed that using all bio-stimulants significantly increased cucumber growth parameters (plant height, stem diameter, leaves number, leaf area, shoot fresh weight, and root fresh weight). Seedlings Vigor Index (SVI) increased multifold compared with control by all treatments. The increase in cucumber seedlings vigor had a highly significant effect compared with control and the increase was 55.9% followed by 55.2% and 53.4% by Put, MT, and EBR treatments respectively. Our study concluded that the application of plant bio-stimulants can be used to modify coco-peat substrate with a positive effect on plant growth and improvement of cucumber plants under soilless culture.
... However, they have an indirect effect, timeconsuming, wasteful, and costly, making humates were preferably added directly into soils as is done with fertilizers (Ibrahim & Ali, 2018). The HS indirectly stimulate the plant growth through modulating some properties of cultivated soil, including the metabolism of microorganisms, nutrients availability, increased pH buffering, cation exchange capacity, and physical structure or directly by increasing biological membrane permeability as well as affecting plant metabolism by acting as hormone-like substances (Trevisan et al., 2010;Muscolo et al., 2013;Rose et al., 2014). ...
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TWO field experiments were conducted, during two cropping seasons, to study the cultivation of two lentil cultivars, namely Sina-1 and Giza-9, under a calcareous soils condition. The cultivation was done using liquid crude humates, extracted from compost, as organic fertilizer or consortium of some PGPR including Serratia marcescens, Bacillus megaterium and Pseudomonas fluorescens as biofertilizer against mineral fertilization. The experiments were designed in a split block design. The humate application or PGPR stimulate microbial count and dehydrogenase activity, in the rhizosphere, against a full dose of mineral fertilizers. In general, high rate of humates followed by a full dose of nitrogen recorded maximum values with respect to the plant height, shoot dry weight and leaf area at vegetative state. Concerning to the dark green color index (DGCI), the plants significantly captured more greenness due to applying a full dose of nitrogen followed by a high dose of humate (20L/fed) with Giza 9 compared with Sinai 1 cultivar. The maximum values were recorded by Giza 9 cultivar fertilized with a high dose of humate followed with that of a full dose of nitrogen for pods and seeds number and seeds yield during both cropping seasons. However, the effect of the co-inoculation with PGPR and Rhizobium boosted the yield components against the absolute control and treatment of individual Rhizobium + activation dose of nitrogen for the same parameters. Based on results it may be concluded that cultivation of Giza 9 cultivar with the application of crude humate at 20L/fed and Rhizobium inoculation is being favored under calcareous soil.
... Within the last two decades an impressive body of knowledge on the role of humic substances for nutrient availability in soils and nutrient acquisition by higher plants has been collected showing strong and coordinated effects of humic substances on nutrient uptake by higher plants (see for review Chen et al., 2004a;Pinton et al., 2009;Muscolo et al., 2013;Tomasi et al., 2013;Canellas and Olivares, 2014;Canellas et al., 2015;Nardi et al., 2017;Olaetxea et al., 2018;Zanin et al., 2019;Urrutia et al., 2020). With respect to the Fe and P nutrition, humic substances affect the availability in soil and the acquisition by higher plants by several pathways (Gerke, 1992a(Gerke, , 1992bGerke and Meyer, 1995;Gerke et al., 2000;Pinton et al., 2009;Gerke, 2010;Urrutia et al., 2014;Canellas et al., 2015;Gerke, 2015a;Nuzzo et al., 2018;Zanin et al., 2019;Urrutia et al., 2020). ...
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Humic substances affect iron (Fe) and phosphate (P) uptake by higher plants by two different ways. First, humic substances bind Fe(III) by forming humic‐Fe complexes of medium to high stability. In soils with pH > 5.0 these complexes account for most of the Fe in the soil solution, while dissolved Fe from Fe‐oxides exhibit an extreme low solubility (<< 0.1 µM). Humic‐Fe and humic‐Al complexes may bind P and form humic‐metal‐P complexes in the soil solution. Also, humic substances may desorb P bound to Fe(Al)‐oxides by binding to the P sorption sites of the oxides. These mechanisms may increase soil Fe and P availability. Second, humic substances affect several physiological processes of higher plants which are related to the acquisition of mineral nutrients from soil such as Fe and P. Soil humic substances exhibit plant hormone features, the quality and extend depending on the humic sources, the apparent molecular weight and the association status of the humic substances. They may affect the rooting pattern, the excretion of protons and carboxylic anions, the plasma membrane Fe‐reductase activity and they may activate Fe(II) and P transporters. Organic acid anions released by the roots can decrease the apparent molecular weight of the humic substances which may in turn increase the plant hormone activity of the humics. These mutual interactions can be described as soil‐root cross‐talking or humic acid cross‐interactions with roots.
... In this respect, it has to be noticed that the major part of the plant hormones has acid functionalities. In previous studies a prevalence of carboxyl carbon groups, phenolic moieties and sugars was detected in the larger bioactive fraction of humic acids isolated from different sources, such as recycled biomasses [29][30][31]. ...
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Background Plants primed by humic acids showed physiological and molecular response against different abiotic stresses without the presence of stressor agents (salinity, drought, heavy metal toxicity). It is plausible that humic acids themselves can act as chemical priming substances in plants. We hypothesized that humic acids can trigger the weak acids stress response in cell plants acidifying the cytosol and thus eliciting the transduction signalling response cascade. Methods The dose–response curves of maize seedlings roots with different concentrations of humic, acetic and salicylic acids determined the most active and inhibitory concentration. These data were further used to evaluate changes on intracellular pH using BCECF-AM probe (2,7-bis(2-carboxyethyl)-5(and 6)-carboxyfluorescein, acetoxymethyl ester) and differential transcription level of genes related to weak stress response in plants by qPCR real time. Results Humic acids like short chain organic acids decrease the intracellular pH showed by the increased fluorescence of BCECF probe. The drop in cytosolic pH promoted by humic acids was not transient. We observed a high level of protein kinases related to cell energy-sensing and transcription factors associated to transduction of stress signalling. Conclusion The humic acids can be considered as a chemical priming agent, since in the appropriate concentration they can induce the typical plant abiotic stress response of weak acids inducing plant acclimation and enhancing the abiotic stress tolerance.
... Some of these are naturally friendly bio-stimulants that may enhance crop growth and yield. The most capable selections include humic and fulvic acids (Barakat, Osman, Semida, & Gyushi, 2015;Muscolo, Sidari, & Nardi, 2013), organo-mineral fertilizers (Calvo, Nelson, & Kloepper, 2014;Semida, Abd El-Mageed, Howladar, Mohamed, & Rady, 2015), and biochar (Akhtar, Andersen, & Liu, 2015;Calvo et al., 2014) which can proficiently stimulate plant growth, improve soil fertility, and promote plant tolerance to adverse conditions. A 'Controlled Temperature Biochar Retort for Slow Pyrolysis' (patented) has been developed for the production of standard-quality biochar that can be used to improve both crop yields and soil quality. ...
Article
Global warming and climate alterations have adversely affected the agricultural production systems. The application of biochar can help in mitigating climate change impacts and enhance the production and quality of agriculture. The field experiments were conducted during 2018 and 2019 to evaluate the effects of straw mulch (0 & 8 t ha−1) and biochar (0, 4, 12 & 36 t ha−1) on soil temperature, soil pH, bulk density, electric conductivity, cation exchange capacity, soil organic carbon, soil nutrient status (available P, K, NO3− and NH4+) at various soil depth (10, 20 & 30 cm), and yield and yield‐related traits of rainfed maize. The results showed that addition of biochar regulated the soil temperature, pH, electrical conductivity, cation exchange capacity, and increased the soil organic carbon, soil nutrient status (available P, K, NO3− and NH4+) compared to non‐biochar‐treated soils. In contrast, the higher amount of biochar (36 t ha−1) application decreased the soil bulk density compared to control. However, the combined application of straw mulch and biochar improved the grain yield and yield contributing traits of maize. In conclusion, either straw mulch and biochar or combined straw mulch + biochar‐based soil management techniques regulate the temperature and physiochemical properties of soil. These improvements in soil properties increased the grain yield of rainfed maize and help to mitigate global warming. This article is protected by copyright. All rights reserved
... HS are end products of humification and they are complex and heterogenous mixtures of polydispersed matters as a result of conversion of plant and microbial remains via using some chemical and biochemical reactions (Muscolo, Sidari, & Nardi, 2013). The humic substances have a similar structure with hormones and acting like plant growth hormones that they increase the membrane permeability and provide the transportation of essential elements to the roots, and balance the respiration (Masciandaro, Ceccanti, Ronchi, Benedicto, & Howard, 2002). ...
... There is a notable rise in research work on the usage of naturally produced products to be incorporated in the sustainable agriculture. Many of these bio-stimulants such as humic and fulvic acids, organo-mineral fertilizers and biochar which are environmentally benign are believed to enhance soil fertility, plant growth thus, agronomic productivity apart from abiotic and biotic stress tolerance [1,14,94,125]. As a soil additive generated from waste biomass through pyrolysis, biochar has earned noteworthy consideration as a possible strategy to enhance the management of agriculture soils [99]. ...
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A large number of population in the world is dependent on agriculture and its products. However, with the growing population the need for different agricultural products has increased over a period of time. The agricultural soil has been degraded by the use of synthetic fertilizers. Different methods are developed by the researchers to restore the degraded soil ecosystems. Among the different options available, use of biochar is a viable option. The biochar is carbon rich has emerged as a possible option for restoration of degraded land and to increase agriculture efficiency in numerous frameworks and carbon fixation. This paper is an attempt to study the applications of biochar for the sustainability of agricultural ecosystems.
... Furthermore, application of HS positively influences root growth, especially lateral root emergence and root hair initiation which are involved in plant nutrient uptake (Canellas and Olivares, 2014;Puglisi et al., 2013). At the same time, capacity of HS and HA to stimulate the uptake of nitrate [NO 3 -] (Quaggiotti et al., 2004;Canellas et al., 2010;Muscolo et al., 2013;Rose et al., 2014) is not tested to mitigate the N starvation in sugarcane. ...
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Humic substances (HS) and humic acids (HA) are proven to enhance nutrient uptake and growth in plants. Foliar application of urea combined with HS and HA offers an alternative strategy to increase nitrogen use efficiency (NUE). The objective of this study was to understand the effects of foliar application of HA and HS along with urea on NUE and response of different biometric, biochemical and physiological traits of sugarcane with respect to cultivar, mode of foliar application, geographic location and intervals of foliar application. To study this, two different independent Experiments were conducted in green house facilities at two different agro-climatic zones (USA and Brazil) using two different predominant varieties, modes and intervals of foliar applications. The three different foliar applications used in this study were (1) urea (U), (2) mixture of urea and HS (UþHS) and (3) HA (UþHA). In both Experiments, 15 N (nitrogen isotope) recovery or NUE was higher in UþHS followed by UþHA. However, magnitude of NUE changed according to the differences in two Experiments. Results showed that foliar application of UþHS and UþHA was rapidly absorbed and stored in the form of protein and starch. Also induced changes in photosynthesis, intrinsic water use efficiency, protein, total soluble sugars and starch signifying a synergistic effect of UþHS and UþHA on carbon and nitrogen metabolism. These results showed promising use of HS and HA with urea to improve NUE in sugarcane compared to using the urea alone. Simultaneously, mode, quantity, and interval of foliar application should be standardized based on the geographic locations and varieties to optimize the NUE.
... The nutritional effect of humic substances owed to its metal binding capacity, especially its low molecular weight (LMW) components. There were also direct effects reviewed by Nardi et al. (2002) and Muscolo et al. (2013), showing that partial uptake of humic substances, mostly the LMW components, can promote nutrient uptake through improvements in root morphology and cell membrane functions, and enhance plant physiology and metabolism via hormone-like substances. ...
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The growth performance and trace metal accumulation of pak choi (Brassica chinensis L.) were investigated to evaluate the ameliorative effect of humic acid on molybdenum (Mo) slag-spiked calcareous soil. Calcareous soil spiked with 5.0% (w/w) slag was amended with humic acid derived from leonardite from 0 to 5.0% (w/w). With increasing application rate, humic acid enhanced the antioxidative capacity of pak choi seedling, as indicated by increases in the activities of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) and a decrease in malondialdehyde content; humic acid application also increased total chlorophyll content, leaf area, seedling height, and fresh biomass of pak choi. These stimulation effects started to decrease above 2.5–5.0% application of humic acid. The contents of trace metals (Cu, Mn, Zn, As, Cd, and Pb) in the aboveground part of pak choi seedling generally decreased at low rates (0.5% and 1.0%), and then increased with higher rates (2.5% and 5.0%) of humic acid application. Health risk assessment of trace metals based on target hazard quotient (THQ) suggested that consuming pak choi grown on these soils is safe. Low rate (0.5%) of humic acid reduced the potential health risk, while high rates (2.5% and 5.0%) accumulated trace metals and increased health risk. Humic acid could be added to Mo slag-spiked calcareous soil for the yield and food safety of pak choi, but the overuse of humic acid should be avoided.
... Hay diferentes niveles de aproximación para determinar el efecto like-auxin de las SH (cuantificando las enzimas ATP-asas, su actividad o describiendo la expresión de sus genes, mediante metabolómica, analizando cambios metabólicos en la planta, describiendo cambios en la arquitectura de la raíz, mediante mediciones del crecimiento y proliferación de raíces y de la biomasa de la planta en general); así se ha descrito la bioactividad de una gran variedad de AH obtenidos de diferentes fuentes por el método convencional de extracción alcalina y se ha concluido que la bioactividad está relacionada con las características estructurales de las supramoléculas húmicas (Muscolo et al., 2013;Monda et al., 2017) . En trabajos previos se ha evaluado la obtención de SH a partir de CBR mediante la actividad de bacterias solubilizadoras de carbón (BSC) (Valero et al., 2011) y se ha caracterizado la estructura supramolecular de la fracción de AH, concluyendo que presentan algunas diferencias en comparación con los AH obtenidos por el método clásico de extracción alcalina (Valero, 2013), pero aún no se ha determinado si este método de obtención cambia las propiedades bioactivas de los AH, aun cuando preliminarmente se ha encontrado evidencia de bioactividad diferencial de estos AH, mediante el desarrollo de experimentos de fitoestimulación en plantas de maíz (Pantoja et al., 2016). ...
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In this work a rapid test to evaluate the bioactivity of humic acids (HA) obtained from a lignite coal through two methods was tested: 1) through chemical extraction with NaOH (HA-Q), and 2) by activity of a bacterial strain (Enterobacter aerogenes). For this, the capacity of the HAs to enhance cellular elongation in coleoptiles of wheat was determined, as well as the ability to induce root proliferation and elongation on pregerminated seeds; AH concentrations between 2,0 and 120 mg C. L-1 were tested with reference to the effect enhanced by an AIA 2,0 mgL-1 solution. It was found that treatment with AH-Q at 40 mg C.L-1 enhance a greater elongation of coleoptiles and roots, whereas a concentration of 20 mg C.L-1 of AH-B enhanced highest bioactivity in all growth parameters evaluated. The results indicate that the evaluated HAs exhibit bioactivity that depends on the type of extraction and on the concentration applied.
... from soil having different carbon sources with similar structures (Muscolo et al., 2013;García et al., 2016a). HS increase the lateral development and formation of root hair (Ramos et al., 2015). ...
Article
Boron (B) is a fundamental micro-nutrient for plants, while deficiency or excess manipulates growth and leads to quality and yield losses. Excess boron (EB) is more difficult to manage in plants compared to deficiency, where it is irreversible. Several strategies have been developed to mitigate EB stress in plants. This review article abstracts the presence of B, its absorption and transport by plants, functions in plant life, its toxicity, physiological responses to it, recent developments in its toxicity alleviation, and provides recommendations for future studies.
Chapter
Food researchers in the present era are encountered by two major challenges that are growing populating and depleting resources keeping in view the increase in food demand, researchers are trying hard to satisfy the needs of the present generation without comprising the availability of natural resources for future generation. Food production has intensified to critical limits adding to irreversible climate change; therefore, the need of time is to look for sustainable alternatives. One such potential solution is the use of bio-stimulants derived that can be obtained from humic substances. These bring about morphological, physiological and molecular changes in plants. These changes positively enhance in uptake of nutrients, their distribution as well as assimilation. Improved metabolism helps in improvement of plant performance and vigour. This chapter will help to understand the potential of using humic substances as bio-stimulants, their role in improvement of plant growth and their benefits for sustainability of agriculture.
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Background The Arctic Ocean receives massive freshwater input and a correspondingly large amount of humic-rich organic matter of terrestrial origin. Global warming, permafrost melt, and a changing hydrological cycle will contribute to an intensification of terrestrial organic matter release to the Arctic Ocean. Although considered recalcitrant to degradation due to complex aromatic structures, humic substances can serve as substrate for microbial growth in terrestrial environments. However, the capacity of marine microbiomes to process aromatic-rich humic substances, and how this processing may contribute to carbon and nutrient cycling in a changing Arctic Ocean, is relatively unexplored. Here, we used a combination of metagenomics and metatranscriptomics to assess the prevalence and diversity of metabolic pathways and bacterial taxa involved in aromatic compound degradation in the salinity-stratified summer waters of the Canada Basin in the western Arctic Ocean. Results Community-scale meta-omics profiling revealed that 22 complete pathways for processing aromatic compounds were present and expressed in the Canada Basin, including those for aromatic ring fission and upstream funnelling pathways to access diverse aromatic compounds of terrestrial origin. A phylogenetically diverse set of functional marker genes and transcripts were associated with fluorescent dissolved organic matter, a component of which is of terrestrial origin. Pathways were common throughout global ocean microbiomes, but were more abundant in the Canada Basin. Genome-resolved analyses identified 12 clades of Alphaproteobacteria , including Rhodospirillales , as central contributors to aromatic compound processing. These genomes were mostly restricted in their biogeographical distribution to the Arctic Ocean, and were enriched in aromatic compound processing genes compared to their closest relatives from other oceans. Conclusion Overall, the detection of a phylogenetically diverse set of genes and transcripts implicated in aromatic compound processing supports the view that Arctic Ocean microbiomes have the capacity to metabolize humic substances of terrestrial origin. In addition, the demonstration that bacterial genomes replete with aromatic compound degradation genes exhibit a limited distribution outside of the Arctic Ocean suggests that processing humic substances is an adaptive trait of the Arctic Ocean microbiome. Future increases in terrestrial organic matter input to the Arctic Ocean may increase the prominence of aromatic compound processing bacteria and their contribution to Arctic carbon and nutrient cycles.
Article
Increasing global demand for food production, often exasperated by excessive use of chemical fertilizers, has led to deterioration of soil health. Immediate action is needed to restore soil health in a sustainable manner. This review advocates switching to use of more organic matter (manure and compost) that contain vital nutrients for plant growth and help restore soil health. One important source of organic matter found ubiquitously in nature is humic substances, which are derived from degraded plant remains and their application to soil enhances essential nutrient supply and assimilation of atmospheric carbon dioxide (CO2) due to increased biomass yield. Promoting this globally can then lower atmospheric concentrations of carbon dioxide and create a sustainable agricultural practice. However, the process of humification and molecular structure of HSs remains a little understood subject of soil science. Therefore, it is imperative to understand the mechanism of various roles of HSs in agroecosystems. This review offers an insight into the various structural and functional aspects of HSs, particularly the humic acids (HAs). The dynamic and interactive nature of HSs creates the framework of sustainable agriculture.
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As substâncias húmicas (SH) contribuem para o crescimento e o desenvolvimento de diferentes espécies vegetais. Existem relatos de efeitos positivos das SH sobre o desenvolvimento de várias espécies vegetais importantes para a produção de alimentos, fibras e energia (GUO et al., 2019). O efeito positivo da aplicação de SH na promoção do crescimento de plantas e na redução da intensidade de algumas doenças de natureza biótica têm levado a um crescente interesse sobre o tema e ao aumento das pesquisas visando o seu uso na agricultura (AGUIAR et al., 2013a; BONANOMI et al., 2018). Nesta década, foram intensificados os estudos sobre as SH incluindo a busca de técnicas capazes de controlar a sua atividade e a elucidação de sua complexidade estrutural (CANELLAS et al., 2012; MORA et al., 2012). As SH se comportam como bioefetores rizosféricos, estimulando algumas atividades bioquímicas e fisiológicas das plantas (SPACCINI et al., 2018), além de desempenharem importante papel sobre as características químicas, físicas e biológicas do solo, resultando em uma ação indireta sobre o desenvolvimento e desempenho das culturas (KHALED; FAWY, 2011). A extensa quantidade de trabalhos e estudos envolvendo SH revelam um indiscutível interesse sobre os seus efeitos positivos nos atributos dos solos e no desenvolvimento das plantas (CANELLAS; SANTOS, 2005; GARCÍA et al, 2019; KHALED; FAWY, 2011). Mas, embora a sua bioatividade nas plantas seja inquestionável, não há um consenso sobre o seu modo de ação (GARCÍA et al, 2018). A atividade biológica das SH está diretamente associada à sua origem, tamanho molecular, composição, estrutura e concentração. Dessa forma, a relação entre a bioatividade e as características das SH precisa ser mais elucidada, a fim de viabilizar o desenvolvimento de tecnologias que direcionem sua aplicação na agricultura e no manejo e conservação dos ecossistemas naturais (AMERI; TEHRANIFAR, 2013).
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У колективній монографії викладено результати досліджень щодо відновлення техногенно забруднених територій і створення сталих екосистем. Розглянуто проблеми та перспективи екологізації сільськогосподарського виробництва для відтворення сталих екосистем. Розкрито питання ефективного використання природно-ресурсного потенціалу сільських територій у контексті екологізації та енергозбереження. Наведено напрями та підходи щодо збереження та відновлення природно-ресурсного потенціалу сільських територій. Досліджено інноваційні екологоорієнтовані підходи у відновленні техногенно забруднених територій і розвитку сільських територій. Визначено напрями екологізації методів переробки сільськогосподарської продукції у забезпеченні продовольчої безпеки України.
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This article studied organic fertilizers obtained from physically and mechanically stimulated peat. The conceptual difference of this formulation from analogs lies in its environmental safety, and humates and humic acids are extracted from the feedstock as fully as possible. We studied the effect of pretreatment of seeds with liquid humic fertilizer on plant growth and development, and found that this fertilizer in low concentrations when growing grain and legumes has a positive effect on the water-physical properties of soil, soil and plant microflora, on increasing mobility reserves of nutrients in the soil, as well as to improve the diet of plants. Consequently, the development and implementation of organic safe humic fertilizers is an urgent area for crop production and food production.
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BACKGROUND Humic acid-enhanced urea (HAU) is the top-selling efficiency-enhanced urea in China. Comprehensive investigation into the structure and efficacy of humic acid complex formation with urea (HACU, the main reaction product during HAU's production) is beneficial to clarify the reaction mechanism between humic acid (HA) and urea, as results, further to provide a guidance for the development of high-efficiency HAU. RESULTS HACU showed a discrepant structural and compositional features from raw HA. N content in HACU was 7.3 times greater than that of HA. Several high-resolution analytical methods showed a sharp increase of NH3 in the gaseous product during HACU pyrolysis, suggesting that urea contributed N to HACU. HACU was characterized with significantly few carboxyl groups than raw HA, implying that the carboxyl group was the main group in HA to participate in the reaction between HA and urea. The presence of amide-nitrogen in HACU verified the structure of reaction product. Furthermore, both HACU and HA could enhance the biomass in hydroponically grown maize seedlings, but the highest stimulation for HACU came out when its concentrations were 50–100 mg C L⁻¹, higher than the optimal concentration for HA (25 mg C L⁻¹), attributed to the lower carboxyl group content for HACU to some extent. CONCLUSION During HAU's production, reaction with nitrogen derived from urea to form amide-N decreased the carboxyl groups in HA, leading to higher concentrations for HACU required to achieve the similar bio-efficacy of HA. This article is protected by copyright. All rights reserved.
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Plant biostimulants offer promising opportunities to aid in addressing the challenges faced by contemporary agriculture – maintaining viable yields of high‐quality produce while reducing the environmental footprint of production. Biostimulants have been shown to enhance plant growth, boost yields, and increase crop tolerance to abiotic stress, acting via a number of mechanisms including phytostimulation, biofertilization, and biocontrol. In the European Union, frameworks and industry standards that require rigorous scientific evidence for all claims have been introduced as a requirement for product registration. However, a lack of regulation in many countries, including Australia, has led to significant variation in product quality and inconsistent results in the field, issues that remain to be addressed. As industry develops the next generation of biostimulant products, the potential for synergistic effects when applying different categories of biostimulants in combination has generated particular interest. In the realm of microbial inoculants, the formulation of microbial consortia which look to harness the beneficial action of multiple species is being investigated. The potential for biostimulants to add value to soilless production systems is another area for development in this space. As biostimulants encompass a diverse group of products, this review focuses on three categories: microbial inoculants, humic substances, and seaweed extracts. After summarising the current understanding of how these substances operate, as well as the crop responses they have been shown to elicit, we examine the challenges facing the development of more effective and reliable products and explore some of the key areas for future research.
Article
High concentrations of lead in soil will greatly weaken the stabilization/solidification effect. Humin (HM) is expected to improve this process because it is a neutral, insoluble, porous and green material as well as an eco-friendly adsorbent extracted from natural peat soil. However, HM has not been studied with respect to the stabilization/solidification (S/S) characteristics of potentially toxic element (PTE)-contaminated soil due to its different extraction sources and methods, as well as complex properties. To study these effects, insoluble HM was extracted for treatment of high-lead contaminated soil by cement-based S/S. The experimental results show that HM has a strong adsorption capacity for lead with a maximum adsorption capacity of 200.2 mg kg⁻¹. The negative influence of a high content of lead on the compressive strength over a 0–90-day period is weakened after adding HM to the soil, wherein a competitive mechanism between HM and a high concentration of lead is proposed. The lead leaching concentration of stabilized soil is significantly decreased under different leaching methods from 0 to 60 days and then decreases slowly. The lead speciation results for the stabilized soil determined through the Tessier sequential extraction method show that HM promotes the gradual chemical transformation of lead from exchangeable and carbonate-bound fractions to a more stable state, with respective decreases of 27.5% and 15.1%. In addition, SEM-EDS images show that HM with a high porosity and specific surface area coexists well with cement, which promotes the stabilization of lead. In conclusion, HM contributes to decreasing the mobility and bioavailability of lead and achieving environmental remediation.
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Mangroves are tropical wetlands that are among the most productive ecosystems on Earth which cover up to 75% of the coastlines. Humic substances are the ever-present natural organic compounds, being a major component of organic carbon in the global carbon cycle. The present study focuses on the organic carbon dynamics as well as spectroscopic characterization (UV, FT- IR, and NMR) of humic substances—humic acids (HAs) and fulvic acids (FAs)—isolated from three tropical mangrove sediments representing different environmental settings belonging to Kerala, in the southwest coast of India during a premonsoon sampling conducted in April 2018. The study revealed a higher concentration of HAs than FAs in all the stations which was also complemented by a higher concentration of tannin and lignin as well as TOC. The E4/E6 ratios of FAs were also higher than that of HAs confirming its low molecular weight and less polymerized nature. The FTIR spectrum of both HAs and FAs showed peaks corresponding to the existence of carboxyl, phenol, carbonyl, and amide group. The proton NMR spectrum showed the presence of aliphatic regions slightly more controlled with long chains and/or alicyclic moieties rather than methyl groups which are also supported by the higher hydrogen content in HAs than FAs, and these peaks were absent in FAs. It also showed the presence of more or less common aromatic core involved in unsaturated structures as well as other aromatic groups like phenols and ionized carboxylic groups slightly higher in FAs than in HAs.
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Recently, it is obvious that the recovery of gold from secondary resources has been of great interest due to its high profitability and vast applications. Among many methods available, reductive adsorption is the easiest, cheapest and eco-friendly way for gold recovery. In the present study, an effective and magnetically separable adsorbent, i.e., humic acid-functionalized magnetite (Fe3O4-HA), had been prepared and used for the reductive adsorption of Au(III) ion. The as-prepared Fe3O4-HA was characterized by using a Fourier transform infrared (FTIR) spectrometer, an X-ray diffractometer (XRD), a scanning electron microscopy with an energy dispersive X-ray spectroscopy (SEM-EDS) and a vibrating sample magnetometer (VSM). Quantitative analyses of the total acidity and the content of carboxyl and phenolic –OH groups of HA and Fe3O4-HA were also performed. While the experiment results showed that Fe3O4-HA was optimum in adsorbing Au(III) ion at pH 3.5 with adsorption capacity (b) according to Langmuir isotherm model was 200 mg g–1, the adsorption process followed pseudo-second order with rate constant (k2p) 3.03 × 10–4 g/(mg.min). It was found that the phenolic –OH group of HA was the one responsible for the reduction of Au(III) ion into metallic gold on the surface of the adsorbent, while the carboxyl group was the active site for the adsorption of Au(III) ion. It was revealed that the presence of radical scavenger 2-propanol decreased the adsorption of Au(III) ion and subsequent reduction to Au. Meanwhile, the adsorbent was easily separated from the medium by an application of an external magnetic field.
Article
Here, coal-related humic substances (HSs) were examined to confirm whether sterilization treatments induce their inferior ability to stimulate lettuce in hydroponic cultivations. Interestingly, a drastic reduction in both lettuce biomass and microbial colony-forming units of the crop culture solutions was observed when the autoclaved HSs were treated. Some microbial genera (i.e., Bacillus and Aspergillus) identifiable in the bare HS-treated hydroponic systems were able to be isolated by direct inoculation of bare HS powders on conventional microbial nutrients, supporting that flourishing microbes in the hydroponic cultivations derive from bare HSs-treated. Moreover, coincubation of some isolated bacterial and fungal strains (i.e., Bacillus and Aspergillus genera) from HSs with lettuce resulted in a significant increase in plant biomass and enhanced resistance to NaCl-related abiotic stresses. Microbial volatile organic compounds renowned for plant stimulation were detected by using solid-phase microextraction coupled with gas chromatography-mass spectrometry. It was finally confirmed that the isolates are capable of utilizing carbon substrates such as pectin and tween 20 or 40, which are relevant to those of microbes isolated from peat and leonardite (i.e., HS extraction sources). Overall, our results suggest that microbiological factors could be considered when commercial coal-related HSs are applied in hydroponic crop cultivations.
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Histosols have a high organic matter content and therefore a high variability of structures and chemical functional groups with adsorptive capacity. This study aimed to select the most appropriate models to describe the sorption phenomena of Cu and Pb in Histosols, identify the types of bonds between these metals and soil samples, and assess the influence of soil attributes and soil humic substance structures on these bonds. The Freundlich and Langmuir models were selected based on the values of the corrected Akaike information criterion and variation of Akaike information criterion as the best models for describing Cu and Pb sorption in Histosols. The values of the adsorption coefficients provided by the models indicated that Pb has higher affinity with the studied soil relative to Cu. However, Cu adsorption to soil occurs specifically and Pb is adsorbed nonspecifically. In general, the contents of N and fulvic acids were the factors that most influenced Pb sorption. Pb has a higher association with more aliphatic fulvic character structures, while Cu has a higher association with soil humic character structures. Therefore, compared to Cu, Pb in the studied Histosol has greater bioavailability potential and, consequently, greater risks of contamination and entering the food chain.
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Humic acid (HA) is composed of a complex supramolecular association and is produced by humification of organic matters in soil environments. HA not only improves soil fertility, but also stimulates plant growth. Although numerous bioactivities of HA have been reported, the molecular evidences have not yet been elucidated. Here, we performed transcriptomic analysis to identify the HA-prompted molecular mechanisms in Arabidopsis. Gene ontology enrichment analysis revealed that HA up-regulates diverse genes involved in the response to stress, especially to heat. Heat stress causes dramatic induction in unique gene families such as Heat-Shock Protein (HSP) coding genes including HSP101, HSP81.1, HSP26.5, HSP23.6, and HSP17.6A. HSPs mainly function as molecular chaperones to protect against thermal denaturation of substrates and facilitate refolding of denatured substrates. Interestingly, wild-type plants grown in HA were heat-tolerant compared to those grown in the absence of HA, whereas Arabidopsis HSP101 null mutant (hot1) was insensitive to HA. We also validated that HA accelerates the transcriptional expression of HSPs. Overall, these results suggest that HSP101 is a molecular target of HA promoting heat-stress tolerance in Arabidopsis. Our transcriptome information contributes to understanding the acquired genetic and agronomic traits by HA conferring tolerance to environmental stresses in plants.
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Though the interaction between humic acid (HA) and heavy metals has been widely reported, the effects of HA on the toxicity of heavy metals to plants are still in debate. In this study, the regulation mechanisms of HA on Pb stress in tea plant (Camellia sinensis L.) was investigated through hydroponic experiments, and the experimental results were explained by using transmission electron microscope (TEM), scanning transmission X-ray microscopes (STXM) and isobaric tags for relative and absolute quantitation (iTRAQ) differential proteomics. Significant alleviation of Pb stress was found with HA coexistence. TEM results showed that HA greatly mitigated the damage of cells caused by Pb stress. Compared with sole Pb treatment, the addition of HA increased the contents of pectin and pectic acid in the cell wall by 10.5% and 30.5%, while arabinose (Ara) and galactose (Gal) decreased by 20.5% and 15.9%, respectively, which were beneficial for increasing Pb adsorption capacity of the cell wall and promoting cell elongation. Moreover, iTRAQ differential proteomics analysis proved that HA strengthened the antioxidant system, promoted the synthesis of cell wall, and stabilized protein and sulfur-containing substance metabolism in molecular level. Notably, the concentration of calcium (Ca) in the cell wall of HA coexistence treatment was 47.4% higher than Pb treatment. STXM results also indicated that the distribution of Ca in the cell wall was restored with the presence of HA. This might promote the formation of the egg-box model, thus alleviating Pb stress in cells. Our results reveal the regulation mechanisms of HA on Pb detoxification in plants and provide useful information for improving the safety of agricultural products.
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A humic substance isolated from a forest soil was separated into carboxyl and phenolic fractions by affinity chromatography using a weak-base amine resin. Humic substance and its fractions were analyzed for physical and chemical characteristics. Their biological effects were compared on growth and root development of Arabidopsis thaliana seedlings. A greater degree of aromaticky was observed for the unfractionated humus (FO) and the carboxyl fraction (FI) compared to the phenolic fraction (FU). A high amount of carboxyl carbon and total sugars were detected in the FI fraction. The FII fraction mainly contained fatty acids and phenolic acids. The FO did not affect the growth and the development of Arabidopsis thaliana seedlings, by contrast, the fractions reduced seedling growth inducing a different development of the root system. In particular the FTI fraction, at the highest concentration (5 mg C L -1), strongly inhibited the primary and secondary root length representing an acute stress for plants. Conversely, the reduction of lateral root growth induced by the FI fraction was not dose-dependent and it was mainly addressed to the root elongation rather than to the lateral root number. When FO and its humic fractions were added to the culture medium at the concentration of 5 mg C L -1, a faster root hair differentiation process was observed. The diverse biological effects of the humic fractions utilized may be attributed to the relative content of specific classes of humic components and it may be also explained by the additive or antagonistic interaction of the single chemical compounds.
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Background and aims Besides general effect of organic residues on soil quality and plant crop, hormonal direct effect on plant growth by extracted humic acids of organic materials is interesting and profitable theme. In the present work, we studied on direct interaction between humic acid and root growth, depending on different origin of organic materials. Methods All extracted humic acids of four organic materials (sewage sludge, compost sewage sludge, municipal solid waste, compost municipal solid waste) were characterized chemically by elemental analyses, ion pair chromatography (ICP), size exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (13 C-CPMAS-NMR) and quantification of IAA. Later, different morphological effects on maize (principal root growth, lateral root growth, root area, root mitosic site, root dry weight and H+-ATPase activity of plasma membrane) were analyzed. Results All humic acids samples promoted root growth and proton pump activity in maize vesicles, especially those composted samples, which contained more carboxylic groups and had a more hydrophobic character, produced preferentially morphological and biochemical effects. Conclusion The conformational dynamics of humic hydrophobic associations in the rhizosphere may release auxin-like plant growth promoters and enhance plant biochemical activities. These organic wastes represent a renewable source of humic acid for use as plant root promoter.
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A humic substance was separated into carboxyl and phenolic fractions by affinity chromatography using a weak-base amine resin. The humic extract and its fractions were analyzed for physical characteristics. Their biological effects were compared, at concentrations of 1 and and chemical 5 mg C L(-1), on the growth of callus of Pinus nigra J.F. Arnold. A higher molecular weight and a unfractionated humus and carboxyl fraction greater degree of aromaticity were observed for the than for the phenolic fraction. Spectra from (13)C nuclear magnetic resonance and diffuse reflectance infrared Fourier-transform spectroscopy showed a low content of lignin-derived, aromatic compounds and a high amount of carboxyl C and total sugars in the carboxyl fraction. The phenolic fraction was found to contain high amounts of fatty acids as well as phenolic acids. The unfractionated humus amended only at the lower concentration (1 mg C L(-1)) increased the callus growth and enzyme activities. The carboxyl fraction improved the growth of calluses and increased the levels of enzymatic activities. The phenolic fraction had an inhibitory effect. Thus, the positive biological effects of the humic fractions utilized might be attributed to the relative content of specific classes of humic components, such as a high amount of peptidic, carbohydratic, and carboxylic groups, and low content of phenolic acids and fatty acids. The heterogeneity of humic substances is strongly influenced by the origin, age, and decomposition processes of parent organic materials. Therefore, the diverse amounts of chemical compounds in humus may influence the function of ecosystems in similarly diverse ways.
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To understand if the biological activity of humic substances may be related to their molecular weight or chemical structure, two humic substances, derived from an Ah horizon of uncultivated couch grass [Elytrigia repens (L.) Desv. ex Nevski] and an Ah horizon of forest soil, were extensively characterized by means of different spectroscopic techniques (diffuse reflectance infrared Fourier transform [DRIFT] and H-1 nuclear magnetic resonance [NMR]). The two humic substances, each separated in fractions with low (< 3500 Da) and high (> 3500 Da) relative molecular mass were compared for their effects on Pinus nigra J.F. Arnold callus. Growth of callus, the soluble sugar content, free amino acid pool, and the activities of the key enzymes involved in C and N metabolism were investigated. Callus was grown for a subculture period (28 d) on basal Murashige and Skoog medium plus humic matters with or without different hormones: indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid, or 6-ben-zylaminopurine. The results of H-1-NMR spectra and the DRIFT spectroscopy showed significant differences in the chemical composition between forest and grass humic substances. A large amount of aliphatic and H-sugarlike component and an intense chemical shift of the beta-CH3 region in both grass humic fractions were observed, while high contents of betaine, organic acid, and COOH groups in both forest humic fractions were detected. A different biological activity between the grass and forest humic fractions was also observed. Thus, the different activity of the two humic substances used seems related to the diverse chemical composition rather than to different molecular weights.
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Background and aims Besides general effect of organic residues on soil quality and plant crop, hormonal direct effect on plant growth by extracted humic acids of organic materials is interesting and profitable theme. In the present work, we studied on direct interaction between humic acid and root growth, depending on different origin of organic materials. Methods All extracted humic acids of four organic materials (sewage sludge, compost sewage sludge, municipal solid waste, compost municipal solid waste) were characterized chemically by elemental analyses, ion pair chromatography (ICP), size exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (13C-CPMAS-NMR) and quantification of IAA. Later, different morphological effects on maize (principal root growth, lateral root growth, root area, root mitosic site, root dry weight and H+-ATPase activity of plasma membrane) were analyzed. Results All humic acids samples promoted root growth and proton pump activity in maize vesicles, especially those composted samples, which contained more carboxylic groups and had a more hydrophobic character, produced preferentially morphological and biochemical effects. Conclusion The conformational dynamics of humic hydrophobic associations in the rhizosphere may release auxin-like plant growth promoters and enhance plant biochemical activities. These organic wastes represent a renewable source of humic acid for use as plant root promoter.
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A critical review of 'random coil' and 'self-associating aggregate' models and of earlier concepts of the macromolecular structure of humic substances (HS) is undertaken as a result of the development of more recent information and hypotheses. Initially, the modes of formation of HS are considered and the influence that these might have on molecular properties is discussed. This is followed by an analysis of the strengths and weaknesses of size-exclusion chromatography (SEC) techniques that is central to the studies under consideration. Emphasis is placed on the importance of overcoming interferences, attributable largely to charge and sorption effects, in order to achieve meaningful applications of SEC. An overview is given of the results obtained by SEC and ultracentrifugation studies of a carefully fractionated collection of humic acid samples. The development of the proposal of the flexible, random-coil model for the macromolecular conformation of HS in solution based on this work is described. This is followed by a review of the evidence put forward in support of the 'self-associating aggregate' hypothesis of molecular structure, and emphasis is placed on areas of concern that question the validity of this model. Aspects of the work that require investigation and verification are identified, and proposals are made for the further studies required.
Article
Humic extracts with distinct chemical and physical-chemical characteristics, obtained by various soil extractants and from different sources, were used to study their biological activity. The humic structural features were related to the rate of nitrate uptake by barley seedlings and growth regulation in watercress and lettuce. Chemical analysis of functional groups, molecular weight distribution, and NMR quantitative spectra were used to characterize the humic extracts. Results showed that the most effective humic fraction on both plant nitrate uptake and hormone-like activity had the highest acidic functionality and the smallest molecular size, whereas both the aliphatic and aromatic content of extracts did not appear to play a role. Low molecular size fractions obtained from the original material by disaggregating the humic macromolecule through the formation of a sort of inverse micelle by acetic acid addition, showed results that confirmed the effectiveness of the combination of high acidity and low molecular size in influencing the biological activity of the plant system tested.
Article
An up-to-date resource on natural nonliving organic matter. Bringing together world-renowned researchers to explore natural nonliving organic matter (NOM) and its chemical, biological, and ecological importance, Biophysico-Chemical Processes Involving Natural Nonliving Organic Matter in Environmental Systems offers an integrated view of the dynamics and processes of NOM. This multidisciplinary approach allows for a comprehensive treatment encompassing all the formation processes, properties, reactions, environments, and analytical techniques associated with the latest research on NOM. After briefly outlining the historical background, current ideas, and future prospects of the study of NOM, the coverage examines: The formation mechanisms of humic substances. Organo-clay complexes. The effects of organic matter amendment. Black carbon in the environment. Carbon sequestration and dynamics in soil. Biological activities of humic substances. Dissolved organic matter. Humic substances in the rhizosphere. Marine organic matter. Organic matter in atmospheric particles. In addition to the above topics, the coverage includes such relevant analytical techniques as separation technology; analytical pyrolysis and soft-ionization mass spectrometry; nuclear magnetic resonance; EPR, FTIR, Raman, UV-visible adsorption, fluorescence, and X-ray spectroscopies; and thermal analysis. Hundreds of illustrations and photographs further illuminate the various chapters. An essential resource for both students and professionals in environmental science, environmental engineering, water science, soil science, geology, and environmental chemistry, Biophysico-Chemical Processes Involving Natural Nonliving Organic Matter in Environmental Systems provides a unique combination of the latest discoveries, developments, and future prospects in this field.
Article
Humic acid is readily available from leonardite, a naturally occurring oxidized form of lignite coal. Humic materials have been found to greatly promote root initiation of Pelargonium hortorum cuttings. Sodium humate, humic acid, fulvic acid, and leonardite produced a proliferation of roots at optimum concentrations of 0.05%, 0.05%, 0.05%, and 0.5%, respectively. Pea root tip elongation measurements indicated that the humic materials possess auxin activity.
Chapter
The addition of organic manure maintains and even improves soil fertility. Humus is recognized as one of the major natural resources for agricultural purposes. Positive effects of humic substances (HS) on plant growth demonstrate that in rye plants humic substances have a greater effect on root development than on leaf and stem development. Similar studies carried out with the humic substances labeled with 14C, established whether the positive effect of these substances was only through an indirect effect, that is, superficial physical contact, or direct effect wherever the substances were absorbed and translocated into the plant. Labeled humic substances, above all those with low MW (molecular weight), show their ability to be absorbed by the plant and be translocated into the plant. Integrating inorganic fertilizers with lower energy organic inputs has become evident not just for economical reasons but for environmental questions as well. The chapter describes the necessity to reconsider the indiscriminate use of chemical resources in modern agriculture and to recycle organic wastes, which can affect crop growth and productivity.
Chapter
As the previous chapter testifies, there is a considerable literature to show that under certain conditions, humic substances can influence plant growth. These influences can be conveniently considered as being direct or indirect. An example of the latter would be the complexation by humic substances of a nutrient cation in the growth medium resulting in an enhanced uptake of the nutrient into the plant31,34,53,87,88,152. In contrast, direct effects on plant growth are the result of the humic substances directly interfering with metabolic processes such as respiration or nucleic acid and protein synthesis36,37,42,72,161.
Article
Humic acid is readily available from leonardite, a naturally occurring oxidized form of lignite coal. Humic materials have been found to greatly promote root initiation of Pelargonium hortorum cuttings. Sodium humate, humic acid, fulvic acid, and leonardite produced a proliferation of roots at optimum concentrations of 0.05%, 0.05%, 0.05%, and 0.5%, respectively. Pea root tip elongation measurements indicated that the humic materials possess auxin activity.
Article
The effects of four humic substance (HS) samples, a soil humic acid and two humic acids and one fulvic acid isolated from a composting substrate, were evaluated on the mycelial growth of Fusarium oxysporum f. sp. melonis (FOM) and F. oxysporum f. sp. lycopersici (FOL). In general, any HS treatment reduced significantly the radial growth of the FOM mycelium either in normal [potato dextrose agar (PDA) medium] or sub-optimal (water–agar medium) nutritional conditions. Differently, the FOL growth, which was tested only on PDA, was either inhibited or stimulated on dependence of the HS treatment used. The HS fractions isolated from the composting substrate were the most effective inhibitors of mycelial growth of both fungi. Furthermore, any HS treatment was also able to alter the germination process of FOL in aqueous medium, not only by reducing significantly the number of viable germinating conidia but also by generally decreasing the rate of conidial germ-tube elongation. Apparently, the extent of the inhibitory action was related to some chemical and functional properties of HS, such as the COOH group content and elemental composition.
Article
Slickspot peppergrass (Lepidilllil papilliferum) is a biennial, or possibly perennial, endemic plant growing in the Southern Idaho high desert in visually distinct small-scale depressions in soils that collect water (so-called slickspots). Lepidium papilliferum establishes seed banks not gernlinating the first year but remaining dormant and viable for several years. Humic acids (HA) are universally considered to be the most important, abundant, and biologically and chemically active fractions of soil organic matter and are known to affect plant growth by various mechanisms, depending on their origin, nature, and concentration. The effects of HA in slickspot soils and how they relate to the possibility of being a factor in restoring native plants is only partially known. Thus, the objective of this study was to identify and evaluate the effects of HA isolated from three different layers within the soil profile (silt, vesicular, and clay) from inside a representative slickspot on the gernlination and early growth of slickspot peppergrass. Furthermore, these effects were tentatively related to the chemical, physicochemical, compositional, structural, and functional characteristics of the HA. Results of statistical analysis showed that both the type and concentration of the three HA examined exert a highly significant or significant effect on the germination and early growth of slickspot peppergrass as a function of the soil depth from which the HA originated in the slickspot. In particular, gernlination seemed to be enhanced, especially at higher concentrations, by the less hydrophobic HA, rich in oxygen and total sugars, present in the bottom clay soil layer, whereas root growth and shoot growth were positively influenced by the more hydrophobic and probably more polycondensed HA, rich in C, H, N, and phenolic OH present in the top layer rich in silt.
Article
A humic acid (HA) isolated from a volcanic soil was separated in three fractions of decreasing molecular size (I, II and III) by preparative high performance size exclusion chromatography (HPSEC). The molecular content of the bulk soil HA and its size fractions was characterized by pyrolysis-GC-MS (thermochemolysis with tetramethylammonium hydroxide) and NMR spectroscopy. All soil humic materials were used to evaluate their effects on the enzymatic activities involved in glycolytic and respiratory processes of Zea mays (L.) seedlings. The elementary analyses and NMR spectra of the humic fractions indicated that the content of polar carbons (mainly carbohydrates) increased with decreasing molecular size of separated fractions. The products evolved by on-line thermochemolysis showed that the smallest size fraction (Fraction III) with the least rigid molecular conformation among the humic samples had the lowest content of lignin moieties and the largest amount of other non-lignin aromatic compounds. The bulk HA and the three humic fractions affected the enzyme activities related to glycolysis and tricarboxylic acid cycle (TCA) in different ways depending on molecular size, molecular characteristics and concentrations. The overall effectiveness of the four fractions in promoting the metabolic pathways was in the order: III>HA>II>I. The largest effect of Fraction III, either alone or incorporated into the bulk HA, was attributed to a flexible conformational structure that promoted a more efficient diffusion of bioactive humic components to maize cells. A better knowledge of the relationship between molecular structure of soil humic matter and plant activity may be of practical interest in increasing carbon fixation in plants and redirect atmospheric CO2 into bio-fuel resources.
Article
Humic substances (HS), as component of soil organic matter, have been widely studied. Their positive effects on plant physiology have been further demonstrated, but there are no clear evidences about the direct as well as indirect mechanisms regulating these processes.In this paper a transcriptomic approach based on the detection of cDNA-AFLP markers was used to identify candidate genes potentially involved in the regulation of the response to HS in Arabidopsis thaliana.Using 160 primer combinations, the cDNA-AFLP enabled to identify 133 genes putatively involved in plant–HS interaction. Sequence analysis and Gene Ontology classification indicated that a large number of genes involved in developmental and metabolic processes, as well as in transcription regulation or RNA metabolism were identified as HS-regulated. Real-Time PCR analyses confirmed transcription levels of 32 HS-regulated genes.This study demonstrates that HS exert their effects on plant physiology by means of complex transcriptional networks. From the overall transcriptomic results we may hypothesize that HS exert their function through a multifaceted mechanism of action, partially connected to their well demonstrated auxin activity, but involving also IAA-independent signalling pathways.
Article
The effects of humus on plant metabolism are conditioned by the release of the hormone-like activities contained in HEf bound to HSp. HEf and HSp are both humic fractions that can be separated from each other by acidification with acetic acid or other organic acids. HEf is composed of small molecules and shows hormone-like activities; HSp possesses higher molecular weight and works as a support for HEf. The molecular sizes of the separated HEf and HSp are both low enough to permit root absorption. The dispersion and solubilization of humic molecules are essential to the release of cytokinin-like activity from HSp, but are only preliminary to the release of auxin- and gibberellin-like activities. These can be released by a partial acidification of the humic extracts that do not result in complete depolycondensation. The process appears to regulate the delivery of the hormone-like substances and is influenced by their particular arrangement in the humic aggregate. Key words: Humus fractions, biological effect, nitrate uptake, hormone-like activity
Article
Auxin and cytokinin bioassays were performed to test the biological activity of soluble humic complexes (SHC). 'Pea split stem curvature' (auxin test) and 'cucumber' tests (cytokinin test) did not show any quantifiable activity of SKC. 'Cress test' and 'senescence test' offered good evidence of a hormonal-like activity 100 times lower than that of IAA (1-mg IAA.g-1 SHC) and 10 times lower than that of N6 BA (100mg N6 BA.g-1 SHC). At a high concentration of SHC, toxic effects were evident, indicating the presence of inhibitory substances which counteracted the hormone-like activity of humic complexes. -Authors
Article
14C-labelled soil organic matter (SOM) is taken up by pea roots under axenic conditions. After 18 h of culture, more fulvic acid or water-boiled-soluble soil components are taken up by the tissue than humic acid. The uptake is due to the SOM being adsorbed on to the roots surfaces and cell walls as well as to a process dependent on metabolism, probably protein synthesis. Studies using gel filtration show that humic acid comprises two discrete classes of brown substances based on mol. wt. separation, one >50 000 daltons and the other <2500 daltons. Fulvic acid and water-boiled-soluble material have components of mol. wt <25OO daltons only. Only the low mol. wt. materials are taken up by a mechanism dependent on metabolism irrespective of the soil fraction from which they are derived.
Article
The effects of neutralized solutions of soil humic acids on the activities of a range of proteolytic enzymes and of tyrosinase have been measured. Humic acids inhibit carboxypeptidase A, chymotrypsin A, pronase, and trypsin activities, stimulate papain, ficin, subtilopeptidase A, and thermolysin activities, and had no effect on phaseolain and tyrosinase activities. Stimulation of papain and ficin activities is not due to formation of metal ion-humic acid complexes. Inhibition of trypsin activity and stimulation of papain activity increased with increasing molecular weight of the humic acid. However, humic acid fractions of varying molecular weights had similar effects on the magnitude of inhibition of pronase and carboxypeptidase A activities. Polycondensates derived from p-benzoquinone and catechol influenced enzyme activity in the same way as humic acids, although the order of their relative effectiveness changed with different enzymes. Polyacrylate preparations were the most effective inhibitors of trypsin activity but had no effect on papain and ficin activities.
Article
While earthworms are known to improve plant growth by improving the structure of the soil, recent work has suggested that earthworms also produced humic substances endowed with hormone-like activity. Suspensions of Daucus carota (carrot) cells were treated with auxin derivatives (2,4-D=2,4-dichlorophenoxyacetic acid, IAA=indole-3-acetic acid and NAA=1-naphthylacetic acid) and a humic substance of low molecular weight (HEf), obtained from the faeces of the earthworms Nicodrilus caliginosus and Allolobophora rosea, which have auxin-like activity. HEf, at a concentration of 200 μg C l−l, caused an increase in carrot cell growth, determined by packed cell volumes, similar to that of 2,4-D, and morphological changes induced by HEf were similar to those induced by IAA. Humic matter and the tested auxin derivatives stimulated carrot cell glutamate dehydrogenase (GDH), glutamine synthetase (GS) and malic dehydrogenase (MDH) to various extents. When carrot cells were treated with HEf or IAA, GDH and MDH isoenzymes separated by isoelectrofocusing showed similar polymorphism. The addition of HEf or auxin derivatives to carrot cells caused an increase in free amino acids belonging to the oxaloacetate and α-ketoglutarate pathways. Our results showed that HEf affects nitrate metabolism, has auxin-like activity, was strongly acidic and had elevated peptide, carbohydrate and aliphatic C contents. Our work has confirmed that the effective materials in the HEf were highly acidic and of low molecular weight. We conclude that, in addition to the already well established modes of action, earthworms are important in humogenesis because their faeces contained humic substances that can influence plant growth via physiological effects.
Article
Humic acid solutions, at concentrations as low as 5 mg/1, stimulated by 80–100 per cent invertase development in beet storage disks aged under aseptic conditions. Changes in respiration, RNA content and cell-wall nitrogen were stimulated by less than 20 per cent. Invertase development was not stimulated in the stem storage organs of artichoke and potato. Humic acid ash did not stimulate invertase development which is, therefore, probably due to the organic moiety of the humic acid. Gel filtration studies indicated that fractions having a MW < 50,000 were active in promoting the stimulation. The amount of humic acid taken up by the disks was only 15–20 μg/g fresh weight of tissue after 3 days ageing.Several model humic acids, with ash content about 0·1 per cent stimulated invertase development, but examination of infrared and ESR spectra failed to show any correlation between the basic structure and effect on invertase stimulation. Several humic acid-like fungal pigments were also active in stimulating invertase development.
Article
Humic acid fractions of different molecular weights inhibit IAA-oxidase activity to varying extents. The higher the molecular weight, the lower the IAA-oxidase inhibition; the parent material, however, having the greatest effect. A direct relationship was found between the degree of enzyme inhibition and the number of phenolic groups, C/H ratio and the carbon and nitrogen contents of the humic acid fractions, whereas the relationship was negative for oxygen and hydrogen percentages. The ash content of the humic acid preparations was not related to their effects on the enzyme. These results seem to suggest that phenolic groups, not carboxyl groups, are responsible for the influence of humic acids on enzyme activity.