Mitigation of drought stress in wheat by Bacillus xiamenensis and Bacillus gibsonii through improved growth, nitrogen dynamics, and urease activity

Drought stress is a major abiotic constraint that limits crop productivity by reducing photosynthesis, chlorophyll content, nitrogen uptake, and soil microbial activity. Plant growth-promoting rhizobacteria (PGPR) offer a promising strategy to mitigate these adverse effects. However, limited information is available on the integrated role of Bacillus xiamenensis and Bacillus gibsonii in regulating nitrogen dynamics and urease activity for improving wheat growth under drought conditions. This study was conducted with the hypothesis that consortia inoculation of B. xiamenensis and B. gibsonii would be more effective than individual application in enhancing wheat growth under drought stress. The novelty of the present study lies in elucidating the role of these bacterial strains in regulating nitrogen dynamics and urease activity to alleviate drought stress in wheat. Therefore, total three water regimes were established: control (0% stress; 75% FC), mild drought stress (40% reduced water from 75% FC, i.e., ~ 45% FC), and severe drought stress (80% reduced water from 75% FC, i.e., ~ 15% FC). Each treatment (no strain, B. xiamenesis and B. gibsonii) was applied under a completely randomized design (CRD) in three replicates. Inoculation with B. xiamenensis significantly alleviated drought-induced constraints in wheat by enhancing nitrogen acquisition, and soil urease activity. Under 40% drought stress, B. xiamenensis increased chlorophyll a (52%), total chlorophyll (66%), net photosynthesis (73%), shoot nitrogen (53%), and soil urease activity (79%) over control. Under severe stress (80%), B. xiamenensis also enhanced chlorophyll a (44%), net photosynthesis (95%), shoot nitrogen (74%), and soil urease activity (105%) over control. This suggests a strong linkage of nitrogen uptake and soil urease activity with improved wheat growth. In contrast, B. gibsonii also improved these physiological and soil urease activity but to a lesser extent than B. xiamenensis. In conclusion, B. xiamenensis proved more effective than B. gibsonii in mitigating drought stress in wheat by improving nitrogen uptake, and soil urease activity under drought stress. These findings directly align with the study objective of evaluating rhizobacterial effects under drought stress and confirm the superior performance of B. xiamenensis in sustaining physiological and biochemical processes. Future studies should validate these results under field conditions and further investigate the molecular mechanisms involved in rhizobacteria-mediated drought tolerance.