Response of wild Pistachio seedlings to inoculation with microorganisms under two moisture levels in greenhouse

Wild Pistachio (Pistacia atlantica var. mutica Rech. f.) is an important tree species in the forests of Iran that has faced many challenges in its natural restoration. This study investigated the interaction effects of Funneliformis mosseae, MycoRoot biofertilizer, and Pseudomonas fluorescens on Pistacia atlantica seedlings under two water treatments: 100% field capacity as a non-stress treatment and 50% field capacity as a drought stress treatment. Decreased soil moisture reduced the growth (root collar diameter, shoot and root fresh weight, shoot dry weight) of Pistacia atlantica seedlings. The interaction of mycorrhizal fungi and phosphate-solubilizing bacteria on seedling growth, as well as chlorophyll, carotenoid, and leaf proline content, was significant at the 5% level. The highest stem height was observed in the combined treatment of Funneliformis mosseae and Pseudomonas fluorescens (24.54 cm) under non-stress conditions, while the shortest belonged to the control treatment (8.8 cm) under drought stress conditions. Proline content in seedlings inoculated with Funneliformis mosseae in the presence of Pseudomonas fluorescens was higher (8.87 μmol/g) than other treatments, and this treatment was more effective in reducing drought stress symptoms than other treatments. Under non-stress conditions, the presence of Pseudomonas fluorescens alone did not play a significant role in improving seedling growth, but its positive effects on growth appeared when interacting with mycorrhizal fungi and during drought. Although this research observed that mycorrhizal and bacterial seedlings had better growth than control seedlings and that microorganisms had the same effect as irrigation on some growth characteristics, it is necessary to conduct similar additional experiments in nurseries and natural habitats on P. atlantica seedlings using different irrigation levels to confirm these results.