Antonella Vitti, Leonardo Coviello, Maria Nuzzaci, Giovanni Vinci, Yiannis Deligiannakis, Evangelos Giannakopoulos, Domenico Ronga, Alessandro Piccolo, Antonio Scopa, Marios Drosos
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Greater root hairs density and dry matter, compared to control, were observed using concentration of 5 mg L<sup>−1</sup> for HALP, 50 mg L<sup>−1</sup> for LHA, and 100 mg L<sup>−1</sup> for SHA. The germination index was the largest (698% more effective than control) with 50 mg L<sup>−1</sup> of SHA, while it was 528% for LHA, and 493% for HALP at 5 mg L<sup>−1</sup>. SHA contained the lowest aromatic and phenolic C content, the largest pK<sub>2</sub> value of 9.0 (7.7 for LHA and 7.6 for HALP), the least ratio between the aromaticity index and lignin ratio (ARM/LigR) of 0.15 (0.66 for LHA and 129.92 for HALP), and at pH 6.3 the lowest amount of free radicals with a value of 0.567 × 10<sup>17</sup> spin g<sup>−1</sup> (1.670 × 10<sup>17</sup> and 1.780 × 10<sup>17</sup> spin g<sup>−1</sup> for LHA and HALP, respectively), with the greatest g value of 2.0039 (2.0035 for LHA and 2.0037 for HALP).</p><h3>Conclusions</h3><p>The overall chemical structure of humic acids exerted a biostimulation of cress plantlets. The level of the intrinsic stable free radicals identified by EPR in the humic acids resulted well correlated to the ARM/LigR ratio calculated by NMR. Our results suggested that HA biostimulation effect is related to its applied concentration, which is limited by its free radical content. The modulation of the humic supramolecular structure by ROS and organic acids in root exudates can determine the release of bioactive humic molecules. When the content of the intrinsic humic free radicals is high, possible molecular coupling of the bioactive humic molecules may hinder their biostimulation activity. In such cases, a low humic acid concentration appears to be required to achieve the optimum biostimulation effects.</p><h3>Graphical Abstract</h3>\n<div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":512,"journal":{"name":"Chemical and Biological Technologies in Agriculture","volume":"11 1","pages":""},"PeriodicalIF":5.2000,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://chembioagro.springeropen.com/counter/pdf/10.1186/s40538-024-00613-w","citationCount":"0","resultStr":"{\"title\":\"Biostimulation of humic acids on Lepidium sativum L. regulated by their content of stable phenolic O⋅ radicals\",\"authors\":\"Antonella Vitti, Leonardo Coviello, Maria Nuzzaci, Giovanni Vinci, Yiannis Deligiannakis, Evangelos Giannakopoulos, Domenico Ronga, Alessandro Piccolo, Antonio Scopa, Marios Drosos\",\"doi\":\"10.1186/s40538-024-00613-w\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><h3>Background</h3><p>Humic acid affects plant growth. 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The modulation of the humic supramolecular structure by ROS and organic acids in root exudates can determine the release of bioactive humic molecules. When the content of the intrinsic humic free radicals is high, possible molecular coupling of the bioactive humic molecules may hinder their biostimulation activity. 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Biostimulation of humic acids on Lepidium sativum L. regulated by their content of stable phenolic O⋅ radicals
Background
Humic acid affects plant growth. Its source and structure may play a central role to its functionality. The relationship between humic acid and plant bioactivity is still unclear. This study investigated the biostimulation effects of two natural humic acids derived from soil (SHA) and lignite (LHA) on Lepidium sativum in comparison to a synthetic humic acid model (HALP) with known structure.
Results
All humic acids positively affected cress seed germination and root elongation. Greater root hairs density and dry matter, compared to control, were observed using concentration of 5 mg L−1 for HALP, 50 mg L−1 for LHA, and 100 mg L−1 for SHA. The germination index was the largest (698% more effective than control) with 50 mg L−1 of SHA, while it was 528% for LHA, and 493% for HALP at 5 mg L−1. SHA contained the lowest aromatic and phenolic C content, the largest pK2 value of 9.0 (7.7 for LHA and 7.6 for HALP), the least ratio between the aromaticity index and lignin ratio (ARM/LigR) of 0.15 (0.66 for LHA and 129.92 for HALP), and at pH 6.3 the lowest amount of free radicals with a value of 0.567 × 1017 spin g−1 (1.670 × 1017 and 1.780 × 1017 spin g−1 for LHA and HALP, respectively), with the greatest g value of 2.0039 (2.0035 for LHA and 2.0037 for HALP).
Conclusions
The overall chemical structure of humic acids exerted a biostimulation of cress plantlets. The level of the intrinsic stable free radicals identified by EPR in the humic acids resulted well correlated to the ARM/LigR ratio calculated by NMR. Our results suggested that HA biostimulation effect is related to its applied concentration, which is limited by its free radical content. The modulation of the humic supramolecular structure by ROS and organic acids in root exudates can determine the release of bioactive humic molecules. When the content of the intrinsic humic free radicals is high, possible molecular coupling of the bioactive humic molecules may hinder their biostimulation activity. In such cases, a low humic acid concentration appears to be required to achieve the optimum biostimulation effects.
期刊介绍:
Chemical and Biological Technologies in Agriculture is an international, interdisciplinary, peer-reviewed forum for the advancement and application to all fields of agriculture of modern chemical, biochemical and molecular technologies. The scope of this journal includes chemical and biochemical processes aimed to increase sustainable agricultural and food production, the evaluation of quality and origin of raw primary products and their transformation into foods and chemicals, as well as environmental monitoring and remediation. Of special interest are the effects of chemical and biochemical technologies, also at the nano and supramolecular scale, on the relationships between soil, plants, microorganisms and their environment, with the help of modern bioinformatics. Another special focus is the use of modern bioorganic and biological chemistry to develop new technologies for plant nutrition and bio-stimulation, advancement of biorefineries from biomasses, safe and traceable food products, carbon storage in soil and plants and restoration of contaminated soils to agriculture.
This journal presents the first opportunity to bring together researchers from a wide number of disciplines within the agricultural chemical and biological sciences, from both industry and academia. The principle aim of Chemical and Biological Technologies in Agriculture is to allow the exchange of the most advanced chemical and biochemical knowledge to develop technologies which address one of the most pressing challenges of our times - sustaining a growing world population.
Chemical and Biological Technologies in Agriculture publishes original research articles, short letters and invited reviews. Articles from scientists in industry, academia as well as private research institutes, non-governmental and environmental organizations are encouraged.