(1) Background: Biochar and plant growth-promoting rhizobacteria (PGPR) are widely used as amendments to increase the availability of nutrients and the diversity of the bacterial community within soil. (2) Methods: In this study, we investigated the effects of biochar and PGPR amendments on plant performance, soil physicochemical property, and soil microbial diversity, as well as their relationship in a Eucalyptus (clone DH32−29) plantation in Guangxi, China. We determined the microbial AWCD, Simpson, Shannon, and McIntosh indices, and soil inorganic nitrogen (NH₄⁺, NO₃⁻), total phosphorus (TP), total potassium (TK), total nitrogen (TN), and plant growth and nutrient concentrations; (3) Results: Biochar-only had a significant impact on soil microbial community function, although the effects on plant performance were limited. PGPR plus biochar was found to significantly increase the diversity indices of soil microbes, as well as soil TK and TP. Besides, soil microbes displayed a preference for carbohydrates rather than other carbon sources. (4) Conclusion: Soil microbial functional diversity responded to changes in plant performance and, therefore, it could indicate soil ecological stability and ecosystem productivity. These findings may suggest that biochar and PGPR could potentially maintain ecological sustainability in the soil and improve plant performance through altering soil physicochemical properties in a eucalyptus plantation.

Biochar and plant growth-promoting rhizobacteria (PGPR) are widely used as an amendment for soil physicochemical properties and soil bacterial community diversity. In Guangxi, China, we carried out a study to determine how PGPR and biochar influence the soil’s environmental stability in an Eucalypt plantation. We applied biochar and PGPR in a contrasting application manner to an acidic red loam soil. Thus, three treatments were set up as 5 × 10¹⁰ CFU·mL⁻¹ PGPR-only (MB0), 20 t·hm⁻² biochar-only (B20), and co-application of 20 t·hm⁻² biochar and 5 × 10¹⁰ CFU·mL⁻¹ PGPR (MB20), as well as no biochar and no PGPR (M0B0). Our results indicated that MB20 significantly decreased the soil total nitrogen (TN) and increased the soil total phosphorus (Soil TP), soil ammonium nitrogen (NH₄⁺), and soil water content (SWC) when compared with the control. The MB20 also significantly increased the Simpson, ACE, and Chao indices of the soil bacterial community’s diversity relative to the control. We also observed a significant effect of the Soil TN on both the bacterial community and the functional diversity in soil. These findings may indicate that assessing the soil N status is expected to be an essential indicator of the soil microenvironment’s response to biochar and PGPR applications.