The Effects of Different Inoculant Agents on the Growth of Cymbidium faberi and the Characteristics of Soil Bacterial Communities

This study explored the effects of one mineral fertilizer and two microbial inoculants and their combined applications on soil physicochemical properties, bacterial community structure, and plant growth of Cymbidium faberi under potted cultivation, aiming to provide theoretical and technical support for the sustainable cultivation of ornamental orchids. A single-factor randomized block experiment was designed with eight treatments: control (CK), mineral sulfosulfuric acid potassium (HF), Bacillus subtilis (KC), Trichoderma harzianum (HC), mineral sulfosulfuric acid potassium + Bacillus subtilis (HK), mineral sulfosulfuric acid potassium + Trichoderma harzianum (HH), Bacillus subtilis + Trichoderma harzianum (KH), and mineral sulfosulfuric acid potassium + Bacillus subtilis + Trichoderma harzianum (HKH). Plant growth traits, soil properties, and soil bacterial community characteristics were measured. The effects of inoculant agents on Cymbidium faberi growth, soil environment, and bacterial community, as well as their interaction relationships, were systematically analyzed. The combination of three inoculants significantly promoted plant height and leaf thickness in Cymbidium faberi. Compared with CK, the relative abundance of Pseudomonadota and Bacteroidota in HH treatment increased by 6.0% and 11.0%, respectively, while the relative abundance of Acidobacteriota and Verrucomicrobiota decreased by 6.0% and 12.0%, respectively. Venn diagram analysis revealed 146 ASVs shared among all treatments. KC, HC, and HF had more unique ASVs, whereas HK and HKH had the fewest. Principal component analysis (PCA) was used to visualize differences in bacterial community structure. Significant differences among treatments were confirmed using ANOSIM. Ecological network analysis indicated predominantly positive (cooperative) associations among bacterial taxa, with HKH showing the highest proportion of positive edges, suggesting stronger bacterial cooperation. Correlation analysis showed that Patesibacteria, Acidobacterita, and Planctomycetota were significantly negatively correlated with pH and TP, while Bacteroidota, Actinomycetota, and Methylomirabilota were significantly positively correlated with pH. The Mantel analysis revealed a significant positive correlation between bacterial community composition and richness and pH. Further analysis using the structural equation model revealed that soil nutrients and bacterial communities were the main factors affecting plant growth. This study clarifies the response rules of plant growth, soil physicochemical properties and rhizosphere bacterial communities to different mineral fertilizer and microbial inoculant combinations, and provides a practical basis for the rational screening of functional inoculants and the construction of healthy rhizosphere microecosystems in Cymbidium faberi pot cultivation.