Inconsistent responses of soil bacterial and fungal community's diversity and network to magnesium fertilization in tea (Camellia sinensis) plantation soils

Soil microbes are important drivers of nutrient cycling that regulate plant growth and productivity. Yet, a holistic understanding of the effect of magnesium (Mg) fertilizer on the soil microbial community is still poorly understood. Here, a four-year field experiment was conducted to investigate the impact of different rates of Mg application, including 0, 17.5, 35, 52.5, and 70 kg of MgO ha−1, on soil bacterial and fungal communities (Illumina 16S and ITS amplicon sequencing) associated with tea plantations. Results showed that Mg application significantly increased the soil pH and improved the soil acidity, carbon, and available nitrogen, calcium, and Mg contents. Hence, Mg application also significantly increased soil bacterial diversity but did not affectfungal diversity. Moreover, Mg fertilization increased the relative abundance of beneficial bacterial genera belonging to nitrogen fixation and phosphorus mineralizing groups, such as Gemmatimonas, Rhizomicrobium and Sphingomonas. In addition, the Mg fertilization decreased the relative abundance of some pathogen fungi, such as Pestalotiopsis, Chaetomium, and Coniosporium. Network analysis indicated that the Mg application increased the complexity of the bacterial network by enhancing node numbers and connectivity links, while for fungal networks, the low rate of Mg fertilizer increased total nodes and edges. However, the higher amount of Mg fertilizer decreased the complexity of the fungal network. Correlation analysis between soil properties and microbial communities showed that pH, total carbon and nitrogen, available carbon, and exchangeable Mg were the key soil factors that significantly influenced the microbial community structure. These findings suggest that Mg fertilization could increase soil microbial diversity, alter the microbial structure and improve the microbial network structure of the tea plantation soils. These findings could help to improve soil health, sustainability, and crop productivity. Therefore, Mg fertilization can be considered a viable strategy for improving the health and productivity of tea plantation soils.