Influences of multiple clay minerals on the phosphorus transport driven by Aspergillus niger

Phosphorus (P) is a major limiting nutrient for plant growth. Clay minerals are able to work as active centers in soil system due to their high surface area and CEC. Yet, effects of clay minerals on P biogeochemical cycle driven by microorganisms are still unclear. In this study, hydroxylapatite and three typical clay minerals (kaolinite, palygorskite, and montmorillonite) were incubated with Aspergillus niger to investigate microbial influences on P release and adsorption. Due to the mineral particles, hyphae wrapped small montmorillonite particles (<10 μm, confirmed by SEM and TEM), which promoted microbial bioactivities, e.g., respiration and acid production. P consumption by the fungus lowered the available P from 143 to 68 ppm. Meanwhile, ATR-IR spectra and HPLC analysis confirmed the intense adsorption of oxalic acid (the primary microbial secretion) onto montmorillonite. Despite the higher acid production, both the high adsorption capability of the clay and the acid consumed by phosphate dissolution caused that pH values increased from ~2 to ~4 after montmorillonite addition. In contrast, low CEC, dispersibility, and surface area of kaolinite and palygorskite limited their ability to enhance microbial activities and the subsequent interactions with hyphae. Therefore, clay minerals, especially montmorillonite, can drive P transport with the favor from fungi in ecosystem.