Field Evidence: Microbial Fertilizer Drives Rhizosphere Phosphorus Transformation and Acidity Regulation to Synergistically Promote Chlorogenic Acid Accumulation in Lonicera macranthoides

Microbial fertilizers may improve phosphorus availability and pH in acidic soils, but field evidence linking these changes with medicinal plant biomass and specialised metabolite accumulation remains limited. Here, a one-season field experiment was conducted in acidic yellow soil in Guizhou Province, China, using four fertilization regimes for Lonicera macranthoides: an organic fertilizer plus compound fertilizer control (CK), a bacterial consortium (T1), a simplified bacterial combination (T2), and a fungal agent (T3). Soil chemical properties, soil aggregate composition, flower-bud biomass, and chlorogenic-acid-related compounds were measured. T1 and T3 increased soil available phosphorus and pH at the pre-flowering stage and increased the proportion of water-stable macroaggregates (>5 mm). Both treatments also increased fresh and dry biomass. T1 showed the highest numerical chlorogenic acid content, whereas T3 was more favourable for the accumulation of isochlorogenic acids A and C. Across plot-level observations, available phosphorus was positively correlated with fresh weight (r = 0.804) and dry weight (r = 0.781), and pH was positively correlated with chlorogenic acid (r = 0.687). Univariate regression and redundancy analysis further indicated that available phosphorus and pH were the soil factors most closely associated with biomass and chlorogenic acid accumulation. These findings provide preliminary field indications that microbial fertilizers may improve yield and medicinal quality in acidic-soil L. macranthoides production. However, the single-season, single-site nature of the experiment warrants cautious interpretation and further validation across broader conditions. The observed associations are consistent with, but do not prove, a mechanistic pathway involving microbe-mediated phosphorus transformation and acidity regulation.