Trichoderma enhances salt tolerance in Paeonia ostii ‘Fengdan’ by regulating the rhizosphere soil environment and physiological mechanisms

Aims Salt stress severely constrains the yield of oil peony. Although plant growth-promoting fungi alleviate abiotic stress, the specific mechanisms by which they synergistically enhance salt tolerance through rhizosphere remodeling and physiological regulation remain unclear. Methods We evaluated the efficacy of Trichoderma inoculation on Paeonia ostii ‘Fengdan’ under varying NaCl concentrations (0, 100, 200, and 300 mM) via pot experiments. We comprehensively analyzed plant growth phenotypes, physiological indices, anatomical structures, and rhizosphere soil properties. Results Trichoderma inoculation markedly mitigated salt-induced damage, evidenced by increased biomass, optimized root system architecture (RSA), and enhanced photosynthetic capacity. Physiologically, Trichoderma reduced malondialdehyde (MDA) and ROS content by upregulating antioxidant enzymes and inducing osmolyte accumulation. Anatomically, inoculation maintained the integrity of vascular bundle structures in both roots and stems. Furthermore, Trichoderma colonization significantly improved the rhizosphere microenvironment by decreasing soil pH and electrical conductivity (EC) while stimulating urease, phosphatase, invertase, and dehydrogenase activities, thereby increasing nutrient bioavailability. Conclusions Collectively, Trichoderma confers salt tolerance to P. ostii ‘Fengdan’ through a synergistic mechanism involving the improvement of rhizosphere physicochemical properties, the remodeling of plant anatomical structures, and the activation of physiological metabolism. These findings provide a theoretical basis for cultivating P. ostii ‘Fengdan’ in saline-alkali lands and validate Trichoderma as a high-efficiency bio-inoculant for sustainable agriculture.