Magnesium improves phosphorus availability in the rhizosphere soil of apple by regulating P-cycling microbial communities

As an essential mineral element for plant growth, Magnesium (Mg) is involved in photosynthesis and influences nutrient availability in soil. However, its impact on Phosphorus (P) availability in apple rhizosphere soil and the underlying microbial regulatory mechanism remain unclear. To investigate whether and how Mg enhances soil P availability, this study integrated metagenomics and bioinformatics to assess the effects of Mg on apple plant growth, P accumulation, P availability, microbial community, and phosphorus-cycling genes (PCGs). The results show that Mg significantly increased soil P availability, particularly the labile and moderately labile Pi fractions. Mg-treated groups showed higher diversity and richness of P-cycling microorganisms and distinct microbial community structures. Metagenomic sequencing revealed a greater enrichment of functional genes involved in organic P mineralization (phoD and opd), inorganic P solubilization (gcd), and P transport and regulation (ugpABCE) in Mg-treated groups. Significant positive correlations were observed between soil labile P, moderately labile P, and the abundance of PCGs, as well as between soil exchangeable Mg and P-cycling pathways. These findings suggest that Mg enhances P availability by modulating the P-cycling microbial community. Thus, this study proposes that Mg can serve as a rhizosphere prebiotic to reduce the use of phosphate fertilizer in apple production.