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<p>Polycyclic aromatic hydrocarbons (PAHs) are persistent soil contaminants that induce plant stress. This study assessed how leaf-biomass amendments affect growth and stress-biomarker profiles in <i>Medicago sativa</i> exposed to PAH-contaminated soils.&#xa0;Soils were spiked with 100&#xa0;mg kg⁻¹ pyrene and phenanthrene and amended with 10%, 30%, or 70% (w/w) leaf biomass, sand + 30% amendment, contaminated-only, and non-contaminated controls. After 30 days of soil incubation, residual PAHs were quantified. Subsequently, alfalfa was grown for 4 weeks, and plant vigor, photosynthetic pigments, oxidative stress biomarkers, antioxidant enzyme activities, and nutrient uptake were assessed.&#xa0;PAH dissipation was clearly amendment dependent. The 10% amendment was most effective (18.9 ± 5.85&#xa0;mg kg⁻¹; 81.10% reduction), followed by 30% (33.01 ± 4.92; 66.99%), 70% (39.40 ± 8.05; 60.60%), and sand + 30% (58.10 ± 4.56; 41.90%). The unamended contaminated soil retained its full load (~ 100&#xa0;mg kg⁻¹) as it was not subjected to incubation, whereas the background control declined from 2.82 to 0.50&#xa0;mg kg⁻¹ (82.27% reduction) by natural attenuation. Plant vigor mirrored these trends, highest in controls and lowest in contaminated soil. Stress symptoms included chlorophyll-a depletion, lipid peroxidation, and accumulation of reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂) and superoxide anion (O₂•⁻). Antioxidant defenses—comprising catalase (CAT), which decomposes hydrogen peroxide into water and oxygen; ascorbate peroxidase (APX), which detoxifies hydrogen peroxide via the ascorbate–glutathione cycle; and phenolic compounds, which contribute to non-enzymatic ROS scavenging—were upregulated but insufficient to fully counter oxidative damage.&#xa0;Leaf biomass amendments—particularly at 10%—significantly enhanced PAH dissipation, reduced oxidative stress, and maintained physiological function in <i>M. sativa</i>. These findings support the potential use of leaf residues as low-cost organic inputs for sustainable phytomanagement and highlight <i>M. sativa</i> as a sensitive bioindicator for assessing soil quality in PAH-affected systems.</p> Graphical Abstract <p>Conceptual framework illustrating how leaf-biomass amendments affect growth and stress-biomarker profiles in <i>Medicago sativa</i> exposed to PAH-contaminated soils. Leaf amendment enhances PAH degradation in soil, reducing residual toxicity and improving plant growth, photosynthetic pigments, antioxidant defenses, and nutrient uptake. Higher PAH residues in unamended soils lead to oxidative stress, pigment loss, nutrient deficiency, and reduced vigor. Optimal amendment (10%) provides the best balance for sustainable phytomanagement.</p> <p></p>

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Medicago Sativa Responses to PAH-Contaminated Soils Amended with Leaf Biomass: Growth and Stress Biomarker Assessment

  • 期刊论文

  • 发表日期：

    2026年2月3日

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  • Olanrewaju Roland Akinseye,
  • Charles Knapp,
  • Tatyana Peshkur

摘要

Polycyclic aromatic hydrocarbons (PAHs) are persistent soil contaminants that induce plant stress. This study assessed how leaf-biomass amendments affect growth and stress-biomarker profiles in Medicago sativa exposed to PAH-contaminated soils. Soils were spiked with 100 mg kg⁻¹ pyrene and phenanthrene and amended with 10%, 30%, or 70% (w/w) leaf biomass, sand + 30% amendment, contaminated-only, and non-contaminated controls. After 30 days of soil incubation, residual PAHs were quantified. Subsequently, alfalfa was grown for 4 weeks, and plant vigor, photosynthetic pigments, oxidative stress biomarkers, antioxidant enzyme activities, and nutrient uptake were assessed. PAH dissipation was clearly amendment dependent. The 10% amendment was most effective (18.9 ± 5.85 mg kg⁻¹; 81.10% reduction), followed by 30% (33.01 ± 4.92; 66.99%), 70% (39.40 ± 8.05; 60.60%), and sand + 30% (58.10 ± 4.56; 41.90%). The unamended contaminated soil retained its full load (~ 100 mg kg⁻¹) as it was not subjected to incubation, whereas the background control declined from 2.82 to 0.50 mg kg⁻¹ (82.27% reduction) by natural attenuation. Plant vigor mirrored these trends, highest in controls and lowest in contaminated soil. Stress symptoms included chlorophyll-a depletion, lipid peroxidation, and accumulation of reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂) and superoxide anion (O₂•⁻). Antioxidant defenses—comprising catalase (CAT), which decomposes hydrogen peroxide into water and oxygen; ascorbate peroxidase (APX), which detoxifies hydrogen peroxide via the ascorbate–glutathione cycle; and phenolic compounds, which contribute to non-enzymatic ROS scavenging—were upregulated but insufficient to fully counter oxidative damage. Leaf biomass amendments—particularly at 10%—significantly enhanced PAH dissipation, reduced oxidative stress, and maintained physiological function in M. sativa. These findings support the potential use of leaf residues as low-cost organic inputs for sustainable phytomanagement and highlight M. sativa as a sensitive bioindicator for assessing soil quality in PAH-affected systems.

Graphical Abstract

Conceptual framework illustrating how leaf-biomass amendments affect growth and stress-biomarker profiles in Medicago sativa exposed to PAH-contaminated soils. Leaf amendment enhances PAH degradation in soil, reducing residual toxicity and improving plant growth, photosynthetic pigments, antioxidant defenses, and nutrient uptake. Higher PAH residues in unamended soils lead to oxidative stress, pigment loss, nutrient deficiency, and reduced vigor. Optimal amendment (10%) provides the best balance for sustainable phytomanagement.