Microbial inoculant augments the influence of organic fertilizer on soil microbial communities in tea plantations

With the rapid development of ecological agriculture, microbial inoculants and organic fertilizers have been widely applied in various agroecological systems. Despite the great prospect of microbial inoculants for improving soil fertility and plant growth, it remains poorly understood whether and how microbial inoculants can amplify the effects of organic fertilizers on soil microbial community structures and tea yields. Here, we conducted a field experiment in tea plantations of Rougui and Shuixian cultivars, where the control group only applied organic fertilizer, and the treatment group used a mixed fertilizer (microbial inoculant and organic fertilizer). After four months of fertilization, soil organic matter, total nitrogen, total phosphorus, and alkali-hydrolyzable nitrogen contents were higher in the Rougui tea plantation applied with mixed fertilizer than in the control, whereas these soil nutrients were lower in the Shuixian tea plantation with mixed fertilizer than in the control. PCoA revealed significant separations of soil bacterial and fungal communities between the Rougui and Shuixian tea plantations, and different fertilization regimes in the Rougui tea plantations (p = 0.001). The addition of microbial inoculants enhanced the stochastic assembly processes of both soil bacterial and fungal communities, with the normalized stochasticity ratio of bacterial communities increased by 42.86% one month after the fertilization (p ≤ 0.0001), and that of fungal communities increased by 79.40% after six months (p ≤ 0.0001). Meanwhile, the co-occurrence networks of soil microbial communities treated with microbial inoculants exhibited higher complexity and stronger negative cohesion and robustness. Importantly, the mixed fertilizer increased the yields of fresh teas of Rougui and Shuixian by 83.61% and 11.81%, respectively, compared with the application of organic fertilizer alone, a pattern consistent with elevated stochastic processes and network complexity in soil microbial communities. Overall, this study provides crucial insights into the soil microbial communities' assemblies and network dynamics under different fertilization strategies, which is essential for improving microbial inoculants to further increase the yields of organic tea plantations.