Rhizosphere organic acids drive nutrient release from silicate rock powders across contrasting tropical soils

Aims Silicate rock powders can enhance nutrient availability through rhizosphere-mediated mineral weathering. Although organic acids mediate this process, how soil fertility shapes their interactions with rhizosphere microbial communities and nutrient release remains poorly understood. He, we evaluated how contrasting soil fertility influences rhizosphere organic acids, microbial communities, and nutrient release from silicate rock powders in tropical soils. Methods A 10-month greenhouse experiment was conducted with Urochloa brizantha cv. Marandu grown in low- and high-fertility tropical soils amended with phonolite, diabase, or granite. Rhizosphere organic acids, soil chemistry, plant nutrient uptake, and bacterial and fungal communities were assessed using chemical analyses, high-throughput DNA sequencing, and partial least squares path modeling. Results In low-fertility soil, rock powder reshaped rhizosphere organic acid profiles, increasing their concentrations and improving soil fertility. Organic acids were positively associated with soil fertility indicators and nutrient availability. Path modeling identified organic acids as a central mediator linking rhizosphere biological attributes to improved soil fertility (path coefficient = 0.597, P < 0.01), and plant nutrient uptake (0.671, P < 0.01), whereas fungal community positively influenced organic acid concentrations (0.540, P < 0.05). By contrast, these relationships were substantially weaker in the high-fertility soil, where associations among organic acids, soil properties, and nutrient uptake were reduced, and organic acid concentrations were higher in the control than in rock powder-amended soils. Conclusions Rock powder effectiveness was governed by rhizosphere-mediated processes driven by organic acids, microbial communities, and plant nutrient demand, with the strongest responses occurring in nutrient-limited tropical soils.