Pseudomonas fluorescens Inoculation Enhances Salix matsudana Growth by Modifying Phyllosphere Microbiomes, Surpassing Nitrogen Fertilization

The enhancement of plant growth by soil fertilization and microbial inoculation involves different mechanisms, particularly by altering the phyllosphere microbiome. This study investigated how nitrogen (N) fertilization, Pseudomonas fluorescens strain R124 inoculation and their combined effects influence the growth of different-aged Salix matsudana cuttings by modulating N dynamics within the phyllosphere microbiome. Results showed that P. fluorescens inoculation was significantly more effective than N fertilization alone, enhancing biomass, plant nutrient uptake, soil nutrient content and root development by 90.51%, 18.18%, 72.74% and 126.20%, respectively. Crucially, the inoculation notably shifted the beta-diversity of the phyllosphere microbial community, with K-strategy fungi enhancing plant N fixation and subsequent plant growth. Cuttings from middle-aged forests displayed more robust growth than those from young-aged, associated with a varied impact on phyllosphere fungi, notably increasing the relative abundance of Myriangiales in young (76.37%) and Capnodiales in middle-aged cuttings (42.37%), which improve phyllosphere stability and plant health. These findings highlight the effectiveness of microbial inoculation over N fertilization in promoting plant growth and provide valuable insights for the sustainable management of willow plantations at different stages of development.