Trichoderma harzianum biofertilizer prepared with steam explosion sterilization pretreatment enhancing plant growth and its mechanisms.

The recalcitrant nature of lignocellulosic biomass is a bottleneck hindering its use in high-solid fermentation for the production of biofertilizers. This study employed a steam explosion (SE) sterilization pretreatment (172°C for 2 min and 128°C for 5 min) to enhance the physicochemical properties of lignocellulosic biomass for subsequent fermentation to prepare Trichoderma harzianum biofertilizer and elucidating its mechanisms. Results showed that SE sterilization pretreatment increased wheat straw's specific surface area by 26.1% compared to the conventional thermal sterilization, creating favorable conditions for fungal proliferation. The SE-pretreated medium yielded the highest spore production and elevated levels of growth-promoting factor (indole acetic acid, IAA, 15.0 mg/L) and biocontrol gene expression (Epl1, Sm1) within the T. harzianum biofertilizer. Pot experiments demonstrated that the SE-based T. harzianum biofertilizer significantly enhanced plant growth and antioxidant enzyme activities in both wheat and corn. Correlation analysis revealed positive relationships among T. harzianum proliferation, Epl1/Sm1 expression, IAA levels, and plant growth parameters, providing mechanistic insights into the enhanced efficacy of SE-based biofertilizer. These findings provide an effective SE sterilization pretreatment strategy for improving biofertilizer efficacy while advancing lignocellulosic biomass valorization.