Plant growth-promoting microorganisms and their effects on seed germination in forest tree species: a review

Abstract

Climate change, land use pressure, and low seedling survival rates are affecting forest restoration; therefore, innovative approaches that improve germination and early plant establishment are becoming increasingly important. This review synthesizes current knowledge on the influence of plant growth-promoting microorganisms (PGPM) on seed germination in forest tree species. PGPM, including bacteria and fungi, may influence germination through several mechanisms, such as phytohormone production, nutrient mobilization, stress mitigation, and pathogen suppression. The analysed studies include a wide range of tree species across diverse ecological regions and experimental conditions. PGPM effects on germination vary among specific combinations of host-tree species and microbial strains or consortia. Some studies report significant increases in germination percentage and speed, others show neutral or even negative effects. Bacterial genera such as Bacillus, Pseudomonas, and Azospirillum, along with fungal groups like Trichoderma and mycorrhizal fungi, are among the most frequently studied. Environmental factors, including soil properties, climate, and experimental conditions, strongly influence PGPM performance. Overall, the reviewed evidence indicates that PGPM may improve seed germination in specific host tree or microorganism combinations, particularly under controlled conditions. However, the practical application and selection of microbial strains require careful consideration of the environmental conditions and their effectiveness under field conditions.