Effect of Plant Growth-Promoting Rhizobacteria (PGPR) on Mineral Nutrient Uptake in Persian oak (Quercus brantii L.) Seedlings under Drought Stress

Document Type : Research Paper

Authors

1 Department of Forest Sciences, Faculty of Agricultural, Ilam University, Ilam, Iran.

2 Department of Forest Sciences, Faculty of Agricultural, Ilam University, Ilam, Iran

3 Department of Soil Science Engineering, Faculty of Agriculture, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

4 Department of Environmental Sciences, Faculty of Agriculture and Natural Resources, Yazd University, Yazd, Iran.

5 Department of Forest Sciences, Faculty of Agricultural, Ilam University

Abstract

Drought stress is one of the most important abiotic stresses affecting plant growth, performance, and nutrient balance, leading to reduced seedling quality. This study aimed to evaluate the effect of seed inoculation with selected plant growth-promoting rhizobacteria (PGPR) isolated from native species on mineral nutrient uptake and Dickson Quality Index of Iranian oak (Quercus brantii L.) seedlings under water deficit stress and sustainable nursery management. The experiment was conducted at three levels of water stress (80%, 60%, and 40% field capacity) in a completely randomized design. The effects of PGPR inoculation on the uptake of P, Ca, Mg, Na, and K, K/Na ratio, seedling quality index, and physiological responses were assessed. Results showed that increasing water deficit stress reduced P, Ca, Mg, and Na concentrations and seedling quality, while K concentration and K/Na ratio increased. PGPR inoculation enhanced nutrient uptake, maintained ionic balance, improved seedling quality, and increased seedling resistance under drought conditions. In particular, Bacillus cereus and Bacillus licheniformis increased K, Ca, and Mg content and improved tissue turgor and photosynthesis. A significant positive correlation between seedling quality index and Ca highlighted the key role of this element in structural stability. These findings indicate that PGPR can serve as an effective biological strategy to improve nutrient efficiency, structural quality, and production of drought-resistant seedlings, supporting forest restoration and sustainable natural resource management.

Keywords

Main Subjects

Introduction:

Drought is one of the most critical abiotic stresses affecting plant growth, nutrient uptake, and seedling quality. Plant Growth-Promoting Rhizobacteria (PGPR) have emerged as an effective biological strategy to enhance nutrient uptake, stress tolerance, and structural quality of seedlings. This study aimed to evaluate the effect of seed inoculation with selected native PGPR strains on mineral nutrient uptake and the Dickson Quality Index (DQI) of Iranian oak (Quercus brantii L.) seedlings under water deficit conditions and sustainable nursery management. The results can contribute to producing more resilient seedlings in nurseries and ensuring successful establishment in natural habitats.

Materials and Methods:

The greenhouse experiment involved Iranian oak seedlings subjected to three levels of water deficit: 80% (control), 60% (mild stress), and 40% (severe stress) of field capacity. Bacterial treatments included Bacillus anthracis St2 (B1), B. licheniformis Sk2 (B2), Stenotrophomonas maltophilia Bs1 (B3), B. cereus St3 (B4), a mixture of selected strains (BMix), and a non-inoculated control (B0). Bacterial inocula were grown in NB medium, incubated for 72 h at 28°C, and standardized to 5×10⁹ CFU/ml. Bacterial isolates were collected from rhizosphere and non-rhizosphere soils of oak, Daphne mucronata, and drought-tolerant species Calligonum comosum and Calotropis procera. Screening of isolates was based on drought tolerance, ACC-deaminase activity, IAA production, phosphate solubilization, and HCN production, leading to the selection of four superior strains identified via 16S rRNA gene sequencing. A two-factor factorial completely randomized design with five replications was applied. Seeds were disinfected, germinated, and planted in pots. Each seedling received 5 mL of bacterial suspension, and irrigation was applied daily according to field capacity. After six months, aerial parts were harvested, dried, and analyzed for P, K, Na, Ca, and Mg concentrations. K/Na ratio and DQI were calculated. Data were tested for normality and homogeneity, and two-way ANOVA with Duncan’s test at 5% probability was used to determine the effects of bacterial inoculation, drought stress, and their interactions.

Results:

Bacterial treatments, drought levels, and their interactions significantly affected seedling quality and mineral content. Increasing drought stress reduced P, Na, Ca, Mg, and DQI, whereas K and K/Na ratio increased. PGPR inoculation enhanced nutrient uptake, ionic balance, and DQI. The most pronounced effects were observed in the BMix treatment and strains B2 and B4. Specifically, B. cereus and B. licheniformis increased K, Ca, and Mg concentrations and improved tissue turgor and photosynthesis. Correlation analysis showed a significant positive association between DQI and Ca (r=0.295, p<0.001), highlighting the critical role of calcium in structural stability of seedlings.

Conclusion:

PGPR application is an effective biological strategy for enhancing nutritional efficiency, structural quality, and drought resilience of seedlings. This approach can be integrated into forest restoration programs and sustainable natural resource management to produce high-quality seedlings and support their successful establishment in natural environments

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authorship contribution

M.K., M. H and H.A.; methodology, H.A.; software, M.H. and M.K.; validation, H.A., A.M. and M.K.; formal analysis, M.K.; investigation, M.H and N.P. ; resources, M.K.; data curation, M.K. and H.A.; writing—original draft preparation, M.H., M.K., H.A. and N.P; writing—review and editing, M.H.; visualization, H.A.; supervision, M.H. and M.H.; project administration, M.H.; funding acquisition, M.H. All authors have read and agreed to the published version of the manuscript.” All authors contributed equally to the conceptualization of the article and writing of the original and subsequent

Declaration of Generative AI and AI-assisted technologies in the writing process

The Authors didn’t use AI assisted technologies in this paper.

Data availability statement

Data available on request from the authors.

Acknowledgements

The authors would like to thank Ilam University and Tehran University providing equipments and Facilities.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

The authors declare no conflict of interest.

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Iranian Journal of Soil and Water Research
Volume 57, Issue 2
May 2026
Pages 393-407

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