Biostimulation of humic acids on Lepidium sativum L. regulated by their content of stable phenolic O⋅ radicals

IF 5.2 2区农林科学 Q1 AGRICULTURE, MULTIDISCIPLINARY

Chemical and Biological Technologies in Agriculture Pub Date : 2024-07-25 DOI:10.1186/s40538-024-00613-w

Antonella Vitti, Leonardo Coviello, Maria Nuzzaci, Giovanni Vinci, Yiannis Deligiannakis, Evangelos Giannakopoulos, Domenico Ronga, Alessandro Piccolo, Antonio Scopa, Marios Drosos

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Abstract

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.

Graphical Abstract

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腐殖酸对牛肝菌的生物刺激作用受其稳定酚类 O⋅ 自由基含量的调控

腐殖酸影响植物生长。腐殖酸的来源和结构可能对其功能起着核心作用。腐植酸与植物生物活性之间的关系尚不清楚。本研究对比已知结构的合成腐植酸模型（HALP），研究了从土壤（SHA）和褐煤（LHA）中提取的两种天然腐植酸对莴苣的生物刺激作用。所有腐植酸都对芹菜种子萌发和根系伸长有积极影响。与对照组相比，HALP、LHA 和 SHA 的浓度分别为 5 毫克/升、50 毫克/升和 100 毫克/升时，根毛密度和干物质含量都更高。SHA 浓度为 50 mg L-1 时，发芽指数最高（比对照组高出 698%），LHA 浓度为 5 mg L-1 时，发芽指数为 528%，HALP 浓度为 5 mg L-1 时，发芽指数为 493%。SHA 的芳香和酚 C 含量最低，pK2 值最大，为 9.0（LHA 为 7.7，HALP 为 7.6），芳香指数与木质素比率（ARM/LigR）之比最小，为 0.15（LHA 为 0.66，HALP 为 129.92），pH 值为 6.3 时，自由基数量最少，为 0.567 × 1017 自旋 g-1（LHA 和 HALP 分别为 1.670 × 1017 和 1.780 × 1017 自旋 g-1），g 值最大，为 2.0039（LHA 为 2.0035，HALP 为 2.0037）。腐植酸的整体化学结构对小芹菜具有生物刺激作用。通过 EPR 法鉴定的腐植酸内在稳定自由基的水平与核磁共振法计算的 ARM/LigR 比率密切相关。我们的研究结果表明，HA 的生物刺激效果与其应用浓度有关，而应用浓度又受到其自由基含量的限制。根系渗出液中的 ROS 和有机酸对腐殖质超分子结构的调节可决定生物活性腐殖质分子的释放。当固有腐殖质自由基含量较高时，生物活性腐殖质分子可能发生的分子耦合会阻碍其生物刺激活性。在这种情况下，似乎需要较低的腐殖酸浓度才能达到最佳的生物刺激效果。

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来源期刊

Chemical and Biological Technologies in Agriculture Biochemistry, Genetics and Molecular Biology-Biotechnology

CiteScore

6.80

自引率

3.00%

发文量

审稿时长

15 weeks

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.