Stage-specific application of PGPR, fulvic acid, and chitosan nanoparticles enhances sorghum (Sorghum bicolor L.) tolerance to drought and lead stress

Abstract

Heavy metal contamination, particularly by lead (Pb), and drought stress severely impairs sorghum ( Sorghum bicolor L.) growth and productivity. This study evaluated the efficiency of plant growth-promoting rhizobacteria (PGPR), fulvic acid (FA), and chitosan nanoparticles (Ch − NPs) in mitigating Pb toxicity and drought stress in S. bicolor under a controlled pot experiment. Plants exposed to drought stress (PEG-6000 at − 0.5 MPa) and Pb stress (Pb (NO 3 ) 2 at 100 ppm) showed reduced plant growth, gas exchange parameters, the ascorbate–glutathione (AsA–GSH) cycle, proline metabolism and rhizosphere microbial diversity in S. bicolor . Conversely, drought and Pb stress markedly increased oxidative stress biomarkers, as well as the levels and gene expression of enzymatic and non-enzymatic antioxidants and also health risk indices. The application of PGPR, FA, and Ch − NPs significantly enhanced plant growth and biomass, improved gas exchange traits, increased the activity and expression of both enzymatic and non-enzymatic antioxidants, and microbial diversity and reduced MDA and H 2 O 2 contents. Pb accumulation in S. bicolor declined, and also reduced health risk indices by lowering bioaccumulation and estimated dietary metal intake. Furthermore, these treatments suppressed excessive proline accumulation, and enhanced the AsA–GSH cycle in S. bicolor plants. These findings highlight the potential of PGPR, FA, and Ch − NPs as practical, eco-friendly strategies for improving crop performance under combined drought and heavy metal stress. Future studies may explore their field-level applicability, long-term soil health impacts, and integration with modern sustainable agriculture systems to strengthen crop resilience under changing climate conditions.