Plant growth-promoting bacteria inoculation mitigates drought stress effects in Trifolium pratense L. seedlings

Abstract

Abstract Multiple ecological factors have an effect on the capacity of plants to survive, grow, and produce. In the meantime, a significant limitation on plant growth in dry regions is drought. Accordingly, the study's objective was to determine the impacts of plant growth-promoting rhizobacteria (PGPR) on indices of germination, growth, and nutrient absorption in the red clover (Trifolium pratense L.) under drought regimes. Treatments included different levels of drought: 100% (FC = field capacity), 70% (0.7FC), and 40% (0.4FC) as the first factor and inoculation conditions of PGPRs, including non-inoculation (control), Azotobacter vinelandii (AV), Pantoea agglomerans and Pseudomonas putida (PA + PP), and combined application of Azotobacter + Pseudomonas (AV + PA + PP), as the second factor. Results revealed that the maximum and minimum germination percentages were obtained for interactions of AV + 0.7FC and control + 0.7FC, respectively. The combined treatment of AV + PA + PP had less impact on reducing drought stress on the germination of seeds than the single application of bacteria. Maximum values for length of roots, shoots, and plant’s dry weight were obtained for AV + 0.4FC interaction, while the minimum values were recorded for PA + PP + 0.4FC interaction. Additionally, results showed that the treatment of PA + PP had no significant influence on drought stress reduction (p > 0.05). The highest uptake of K was observed for the treatment of AV + FC, and the highest amounts of Fe and Zn were measured for the interaction of PA + PP + 0.7FC. The lowest uptake was recorded for Fe, Zn, and Mn under the combined treatment of AV + PA + PP + 0.4FC. In general, the use of Azotobacter compared to Pseudomonas had a better effect on reducing drought impacts on plant characteristics and increased plant tolerance to drought stress.