Effects of Artificially Modified Microbial Communities on the Root Growth and Development of Tall Fescue in Nutrient-Poor Rubble Soil

The granite rubble soil produced through excavation during construction is nutrient-poor and has a simplified microbial community, making it difficult for plants to grow and increasing the challenges of ecological restoration. Recent studies have demonstrated that microbial inoculants significantly promote plant growth and are considered a potential factor influencing root development. Microorganisms influence root development either directly or indirectly, forming beneficial symbiotic relationships with plant roots. However, the mechanisms by which microorganisms affect root development and root anatomy, as well as the dynamics of soil microbial communities following the artificial application of microbial inoculants, remain unclear. This experiment utilized granite rubble soil from construction excavation in a pot trial, implementing five different treatment methods. After the fast-growing grass species tall fescue (<i>Festuca arundinacea</i>) was planted, four growth-promoting microbial inoculants-<i>Bacillus subtilis</i> (K), <i>Bacillus amyloliquefaciens</i> (JD), <i>Aspergillus niger</i> (H), and <i>Trichoderma harzianum</i> (HC)-were applied to the soil in the pots. These treatments were compared with a control group (CK) that received no microbial inoculant. At 120 days of plant growth, the composition of the soil microbial community, biomass, root structure, and root anatomy were measured for each treatment group. This analysis aimed to explore the effects of different microbial treatments on the microbial communities and root development of <i>Festuca arundinacea</i> root soil. The study found that the addition of microbial inoculants reduced the number of microbial operational taxonomic units (OTUs) of bacteria and fungi in the soil, affecting both the marker species and their abundance at the phylum level. Additionally, microbial inoculants promoted the development of the tall fescue root structure, increasing metrics such as the total root length, root surface area, root volume, and root-to-shoot ratio per plant. Redundancy analysis (RDA) revealed that the area ratios of various components in the root anatomy of tall fescue's primary roots, such as the root cortex area, stele area, and the number of lateral roots, were influenced by <i>Proteobacteria</i>. <i>Mortierellomycota</i> was found to affect the root epidermis area.