Rock powder type and soil texture shape microbial community shifts and plant biomass responses in highly weathered tropical soils

Silicate rock powders can enhance soil fertility and contribute to carbon sequestration, but their effectiveness depends on the rock type, soil characteristics, and microbial responses. While microbial shifts following rock powder application are reported in subtropical systems, little is known about these dynamics in highly weathered tropical soils with contrasting textures. To address this, we applied three rock powders (phonolite, diabase, and granite) at three doses (1.50, 3.00, and 5.00 Mg ha⁻¹) to sandy and clay tropical soils and evaluated their effects on Urochloa brizantha biomass, soil fertility, and microbial community composition. All rock powders increased plant biomass regardless of application rate, with 5.00 Mg ha⁻¹ significantly enhancing potassium uptake in sandy soil. Bacterial diversity was largely unaffected, whereas fungal communities responded strongly to treatments, indicating that fungi are sensitive indicators of rock powder application. LEfSe analysis revealed distinct microbial enrichments depending on both soil type and mineral amendment. In sandy soils, the application of diabase promoted specific bacterial genera such as Subgroup_7, Actinospica, Ruminiclostridium, and Rhodomicrobium. In contrast, granite amendment selectively enriched fungal taxa in both soil types, including Chaetomium, Aspergillus, Pseudallescheria, and Conoideocrella. These enriched taxa were correlated with plant biomass, potassium uptake, and soil chemical properties, suggesting functional roles in mineral weathering and nutrient mobilization. Notably, plant biomass responses were not directly linked to changes in soil fertility parameters, highlighting the importance of microbially mediated mechanisms. These findings emphasize the need to incorporate mineral-microbe interactions into tropical soil fertility and management frameworks.