Biochar promotes FePO4 solubilization through modulating organic acids excreted by Talaromyces pinophilus

Abstract

Abstract Inoculating phosphate-solubilizing microbes (PSMs) is an effective approach to increasing the soluble phosphorus content in soil for plant growth. While biochar has been shown to promote microbe growth, it can also lead to phosphate precipitation. Therefore, the specific benefits of biochar application for phosphate activation remain unclear. In this study, biochars with varying physicochemical properties were utilized as carriers for microbes. PSMs of Talaromyces pinophilus ( T. pinophilus ) strains were isolated from the rhizosphere soil of corn, radish, and wheat plants, with FePO 4 as the sole phosphorus source. To understand how biochar modulates the phosphate-solubilizing capacity of T. pinophilus , we measured the dissolved phosphate content, strain biomass, and the concentrations of various organic acids excreted by the strains. Our findings suggested that biochar primarily enhanced the phosphate-solubilizing ability of T. pinophilus by stimulating the secretion of organic acids, rather than by increasing strain biomass. The phosphate-solubilizing ability increased by 356% after adding corn straw biochar to the strains isolated from wheat rhizosphere soil. Notably, citric acid showed the most significant correlation with the phosphate-solubilizing ability of the strains. Laboratory-simulated experiments using individual organic acids indicated that the abundant carboxyl groups in citric acid may be a primary property contributing to phosphate release from FePO 4 . This study highlights the essential role of organic acids excreted by PSMs, which are stimulated by biochar, in phosphate solubilization. These findings not only provide valuable insights for optimizing phosphate utilization in the environment but also contribute to the development of biochar-based biofertilizers, advancing sustainable agricultural practices. Graphical Abstract

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