Responses of Rare and Abundant Bacterial Communities to Synergistic Phosphate Fertilization and Trichoderma Inoculation Meant to Improve Alfalfa Yields

In the field of agro-grassland, the synergism of phosphate (P) fertilization and Trichoderma inoculation in alfalfa production and the underlying mechanism of rare and abundant microbes that regulate rhizosphere soil processes in various environments are key but rarely studied topics. Here, we conducted field research through the inoculation/noninoculation of Trichoderma and five levels of phosphorus fertilizer to explore the biological relationships of rhizosphere soil properties, rare and abundant taxa, and alfalfa yields. Our results demonstrate that using Trichoderma inoculation and 15 g/m² of phosphorus fertilizer exhibited optimal alfalfa yield compared with other treatments. alfalfa yields significantly (R² = 0.33; p < 0.001) increased along with soil fertility. Both rare (R_ANOSIM = 0.900; p = 0.001) and abundant (R_ANOSIM = 0.769; p = 0.001) bacterial communities were significantly different under Trichoderma inoculation and P fertilization in a nonmetric multidimensional scaling (NMDS) analysis. Furthermore, different ecological processes dominated the rare and abundant bacterial community assembly. PLS-PM analysis showed that Trichoderma inoculation positively regulated the abundant bacteria community and P fertilization regimes manipulated the rare bacteria community, synergistically contributing to alfalfa yields. Overall, this article believes that inoculation with Trichoderma and appropriate application of phosphorus fertilizer can significantly increase alfalfa yield and affect soil enzyme activity, and the rhizosphere soil abundant and rare bacterial community characteristics have different responses to the synergistic effect of Trichoderma and phosphorus fertilizer. Our research emphasizes the fundamental role of abundant and rare microbes in maintaining crop production using Trichoderma inoculation and P fertilization. Therefore, distinguishing rare and abundant species is beneficial to comprehensively understanding microbial-driven processes and providing theoretical support for maintaining ecosystem productivity.