Bio-organic fertilizer enhances soil mineral solubilization, microbial community stability, and fruit quality in an 8-year watermelon continuous cropping system

Understanding the interaction between microbes and soil nutrients during fertilization is crucial for improving plant fruit quality. However, the impact of soil mineral elements, and their interactions with microbial communities on plant performance remain unclear. In this study, we combined fruit and soil mineral analyses with microbial community resistance assessments in an 8-year watermelon continuous cropping system to investigate the microbiome-mediated plant responses to organic and bio-organic fertilizations. Our results showed that bio-organic fertilizer (BOF) treatment significantly enhanced watermelon quality, with a quality index 1.62 and 9.29 times higher than organic fertilizer (OF) and the control (CK), respectively. BOF improved soil mineral levels, particularly soil available iron (AFe), which was 1.77 and 4.01 times greater than OF and CK, and leaf iron content, which was 2.10 and 11.49 times higher than OF and CK. BOF also improved the soil microbial resistance and microbial community stability along with a promotion of symbiotic components within soil microbiomes and led to a stable microbial community, which supported enhanced soil nutrient cycling and plant health. Additionally, BOF-associated microbial clusters strongly linked with AFe and watermelon quality index. Stable mineral-solubilizing bacteria like Ammoniphilus, Bacillus, Acidibacter, and Talaromyces were enriched by BOF-treatment, which may have contributed to the dissolution of soil minerals (esp., AFe) and watermelon quality. Overall, our findings revealed a significant role of bio-organic fertilizers in improving soil minerals and crop quality through modulating key soil microbial clusters (e.g., stability and symbiont abundances).