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<p>Drought stress is one of the major abiotic constraints limiting the growth and productivity of lettuce (<i>Lactuca sativa</i> L.). This study aimed to evaluate the potential role of zinc oxide nanoparticles (ZnO NPs) and humic acid (HA) in mitigating adverse effects of drought stress on growth, physiological, and biochemical attributes of lettuce. A split factorial experiment was conducted based on a randomized complete block design (RCBD) with three replications, including three irrigation regimes (100, 75, and 50% of field capacity), three levels of ZnO NPs (0, 10, and 30&#xa0;mg L⁻<sup>1</sup>), and three concentrations of HA (0-, 4-, and 6-mL L⁻<sup>1</sup>). The results revealed that drought stress significantly reduced growth parameters, photosynthetic pigments, relative water content, and leaf nitrogen, while it increased electrolyte leakage, proline accumulation, antioxidant enzyme activity, and secondary metabolites such as phenols and flavonoids. Application of humic acid, particularly at 4&#xa0;mL L⁻<sup>1</sup>, markedly improved plant growth, enhanced water status, stabilized cell membranes, and promoted photosynthetic efficiency under both normal and water-deficit conditions. In contrast, ZnO nanoparticles at the applied concentrations showed limited or negative effects, possibly due to suboptimal dosage or unfavorable physiological responses under the tested conditions, and in some cases intensified stress responses. Application of 6- and 4-ml L<sup>-1</sup> HA, respectively improved leaf area by 20% and 15% under 50% FC irrigation. Also, 4 mL L<sup>-1</sup> HA caused a significant increase by 16% in the fresh weight of leaves under 50% FC irrigation and the increases by 25% and 13%, respectively in fresh and dry weights in the control plants. Inclusive, the findings demonstrate that humic acid acts as an effective biostimulant in alleviating drought stress and improving lettuce performance, whereas the application of ZnO nanoparticles requires careful optimization of dosage. Overall, 4 mL L<sup>-1</sup> of HA potentially supports lettuce plants under irrigation deficit and reduces the adverse effects of drought. These results highlight the potential of sustainable inputs such as humic substances for enhancing crop resilience under water-limited conditions.</p>

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Mitigation of drought stress in lettuce (Lactuca sativa L.) through application of zinc-oxide nanoparticles and humic acid: evaluation of growth, physiological, and biochemical indicators

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月24日

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  • Waleed B. M. Allela,
  • Fathel F. R. Ibraheem,
  • Amer M. A. Alramadan,
  • Hussein J. M. AL-Bayati,
  • Zainab Abdulaziz,
  • Zainb. T. Faris,
  • Aya Mohammed Ali,
  • Mohammed. J. Mohammed,
  • Majd M. Yaqoob,
  • Heidar Meftahizade

摘要

Drought stress is one of the major abiotic constraints limiting the growth and productivity of lettuce (Lactuca sativa L.). This study aimed to evaluate the potential role of zinc oxide nanoparticles (ZnO NPs) and humic acid (HA) in mitigating adverse effects of drought stress on growth, physiological, and biochemical attributes of lettuce. A split factorial experiment was conducted based on a randomized complete block design (RCBD) with three replications, including three irrigation regimes (100, 75, and 50% of field capacity), three levels of ZnO NPs (0, 10, and 30 mg L⁻1), and three concentrations of HA (0-, 4-, and 6-mL L⁻1). The results revealed that drought stress significantly reduced growth parameters, photosynthetic pigments, relative water content, and leaf nitrogen, while it increased electrolyte leakage, proline accumulation, antioxidant enzyme activity, and secondary metabolites such as phenols and flavonoids. Application of humic acid, particularly at 4 mL L⁻1, markedly improved plant growth, enhanced water status, stabilized cell membranes, and promoted photosynthetic efficiency under both normal and water-deficit conditions. In contrast, ZnO nanoparticles at the applied concentrations showed limited or negative effects, possibly due to suboptimal dosage or unfavorable physiological responses under the tested conditions, and in some cases intensified stress responses. Application of 6- and 4-ml L-1 HA, respectively improved leaf area by 20% and 15% under 50% FC irrigation. Also, 4 mL L-1 HA caused a significant increase by 16% in the fresh weight of leaves under 50% FC irrigation and the increases by 25% and 13%, respectively in fresh and dry weights in the control plants. Inclusive, the findings demonstrate that humic acid acts as an effective biostimulant in alleviating drought stress and improving lettuce performance, whereas the application of ZnO nanoparticles requires careful optimization of dosage. Overall, 4 mL L-1 of HA potentially supports lettuce plants under irrigation deficit and reduces the adverse effects of drought. These results highlight the potential of sustainable inputs such as humic substances for enhancing crop resilience under water-limited conditions.