Precision magnesium fertilization strategy enhances grapevine (Vitis vinifera L.) yield and quality via boosting leaf photosynthesis and synergizing soil-plant-microbe coordination

Magnesium is an essential nutrient for crop growth and quality. However, its targeted application in fruit production, particularly its comprehensive effects on grapevine performance and the soil ecosystem remains insufficiently studied. To address this issue, a two-year field experiment (2023–2024) was conducted on grapevines ( Vitis vinifera L.) with six Mg(NO₃)₂ application (ranging from 146.0 to 511.0 kg ha⁻¹), with a conventional practice as the control. The application rate of 292.0 kg ha⁻¹ (NMg3) was found to be optimal. This treatment significantly enhanced leaf chlorophyll content and photosynthetic capacity, leading to the most pronounced increase in berry size, weight, and yield. Berry quality parameters, including protein, vitamin C and total sugars, were also the highest under this treatment. Mg application increased total and available nutrient contents (except for available potassium) while lowering soil pH. The soil microbial community structure, dominated by bacterial phyla such as Proteobacteria and fungal phyla such as Ascomycota , was significantly influenced by soil properties. Redundancy analysis identified pH, available potassium (AK), available phosphorus (AP), magnesium content (Mg) and C:N:P stoichiometry as key drivers of microbial community variation. Furthermore, mantel tests and random forest analysis indicated that soil TN was the primary factor influencing yield, followed by total phosphorus (TP), total potassium (TK), ammonium nitrogen (AN), and SOC, whereas TN and AP were key for berry quality. These results demonstrate that optimized magnesium fertilization (292.0 kg ha⁻¹) enhances grapevine productivity and fruit quality through a dual mechanism: a “top-down” effect via enhanced photosynthesis and a “bottom-up” effect by modulating soil nutrient availability and microbiome assembly. This study concludes that precision magnesium management can synchronize soil health with high-yield & quality grape production, underscoring the importance of cultivating a beneficial soil microbiome through balanced nutrient inputs for sustainable viticulture.