Selenium nanoparticles and wheat straw biochar synergistically alleviate combined drought–heat stress in wheat ( Triticum aestivum L.) by modulating antioxidant defense, photosynthetic efficiency, and ion homeostasis

) in a completely randomized design with three replications. Combined DS+HS severely impaired growth, photosynthetic function, and grain yield, while markedly elevating oxidative damage markers and disrupting ionic homeostasis. Notably, combined Se NPs + biochar application produced superior synergistic amelioration relative to either amendment alone, restoring net photosynthetic rate and grain yield to approximately 89%-90% and 88% of control values, respectively, alongside significant reductions in oxidative stress indicators. Gene expression analysis confirmed marked upregulation of key stress-responsive genes (TaSOD1, TaDREB2, TaHSP70, TaNHX1) and coordinated antioxidant enzyme activation. These findings establish that soil co-application of Se NPs and biochar is an effective, agronomically feasible strategy to sustain wheat productivity under the increasingly prevalent combined DS+HS conditions in Pakistan's irrigated cropping systems.