Phosphorus (P) can undergo adsorption and precipitation reactions in the soil. When fixed to iron and aluminum oxyhydroxides in highly weathered soils, P is covalently linked to the soil solid phase and becomes unavailable to crops. Plants and microorganisms produce organic acids as a strategy to acquire P for growth. These compounds have been used to extract P from sparingly soluble phosphate minerals and may play a role in reverting P adsorption and fixation in the soil. The objective of this work was to study the ability of Aspergillus niger FS1 and organic acids to desorb P after 40 d of contact of the nutrient with 75-μm fractions of a typical highly weathered Oxisol. Samples of the soil fractions from the A and B horizons were incubated for 40 d with P at concentrations corresponding to 90% of the soil maximum P adsorption capacity (MPAC). The ability of A. niger FS1 to desorb P from the soil was performed in a culture medium optimized for phosphate-solubilizing microorganisms. The desorption kinetics of the P bound to the soil fractions was evaluated for oxalic acid at 10 mmol L⁻¹, and for a mixture of oxalic + citric acids, both at 5 mmol L⁻¹. Water at pH 7.0 and at pH 2.0 was used as controls. The fungus released 18.0% of the P from the A and B horizon fractions after 7 days of growth. Oxalic acid was the most efficient compound at desorbing P from the soil, releasing 32.7% of the P from the A horizon fraction, and 18.5%, for the B horizon fraction. These findings contribute to a better understanding of the mechanistic basis of microbial P release from highly weathered soils, opening prospects for the development of microbial techniques allowing plant access to P fixed in the soils and the improvement of P fertilizer use efficiency.

磷（P）在土壤中会发生吸附和沉淀反应。当在高风化的土壤中固定于羟基氧化铁和氢氧化铝时，P与土壤固相共价连接，对农作物不可用。植物和微生物产生有机酸作为获取P进行生长的策略。这些化合物已被用于从微溶的磷酸盐矿物中提取磷，并可能在恢复磷在土壤中的吸附和固定中发挥作用。这项工作的目的是研究黑曲霉FS1和有机酸在养分与典型的高度风化的Oxisol的75μm馏分接触40 d后解吸P的能力。将来自A和B层的土壤部分样品与P孵育40 d，其浓度相当于土壤最大P吸附量（MPAC）的90％。黑曲霉FS1从土壤中解吸磷的能力是在针对磷酸盐增溶性微生物进行了优化的培养基中进行的。在10 mmol L ^-1的草酸和5 mmol L ^-1的草酸+柠檬酸的混合物中，评估了与土壤部分结合的P的解吸动力学。。使用pH 7.0和pH 2.0的水作为对照。生长7天后，真菌从A和B水平部分释放了18.0％的P。草酸是最有效的从土壤中解吸磷的化合物，从A水平部分释放32.7％的P，而B水平部分释放18.5％的P。这些发现有助于更好地了解高风化土壤中微生物磷的释放机理，为微生物技术的发展开辟了前景，使植物能够接触固定在土壤中的磷，并提高了磷肥的使用效率。