Purpose Soil acidification and magnesium (Mg) deficiency are common in tea gardens in southern China. The application of Mg fertilizer and biochar combined with fertilizer is considered as one of the effective agronomic measures to improve the soil environment and tea quality. In this study, the effects of application of biochar and Mg fertilizer on soil microbial community, chemical properties, and tea quality in strongly acidic tea gardens were investigated. Materials and methods A pot experiment was designed in a greenhouse with four treatments, namely CK (with no soil amendment), BF (with wood biochar), MF (with Mg fertilizer), and BMF (combined with wood biochar and Mg fertilizer). Soil and tea samples were collected after 1 year of treatment for determination soil chemical properties and tea quality indexes. Bacterial and fungal diversity and communities were determined by high-throughput sequencing technique. Results and discussion The results showed that BMF treatment could significantly increase soil pH from 4.62 to 5.46 and TN and TC contents from 1.75 g center dot kg-1 and 19.12 g center dot kg-1 to 2.18 g center dot kg-1 and 36.28 g center dot kg-1, respectively, compared with CK. In addition, the diversity of soil bacterial and fungal communities increased under BMF treatment, with the relative abundances of bacterial genera (Brevundimonas, Bradyrhizobium, Nitrospira, Acidobacteriota_Gp1, and Devosia) and fungal genera (Plectosphaerella, Mortierella, and Saitozyma) significantly increased. These genera were significantly positively correlated with tea quality. Furthermore, BMF treatment significantly improved tea quality, including tea polyphenols, amino acids, caffeine, and water extract content, with the increasing ratios of 16.46%, 32.67%, 39.22%, and 22.54% compared with CK. Conclusions The results indicated that combined application of biochar and Mg fertilizer to acidic soils in tea garden could alleviate the soil acidification, improve the nutrients availability, increase soil microbial diversity, and promote the relative abundance of beneficial communities, thereby positively improving tea quality. Our research suggest that the co-application of biochar and Mg fertilizer with traditional fertilization is a potential fertilization practice in southern strongly acidic tea gardens.
