Phosphorus availability and fractions responses to chemodiversity of exogenous dissolved organic matter in lime concretion black soil

Abstract The chemodiversity of exogenous dissolved organic matter (DOM) is significantly increased during the composting process, yet its influence on soil phosphorus (P) transformation is uncertain. A 60‐day incubation experiment was conducted to assess the availability and fractions of P in lime concretion black soil in response to exogenous DOM input, with three treatments: control (CK), soil with DOM from 30 days decomposed straw (DOM1) and soil with DOM from 90 days decomposed straw (DOM2). The results demonstrated that the addition of DOM caused an increase in the content of available P in the soil, particularly the addition of DOM1 with more protein‐like substances and a lower degree of humification. Compared to the control, DOM1 and DOM2 treatments showed an increase in available P content of 17.3%–54.3% and 0.6%–18.2%, respectively. However, the response of the soil's physicochemical and biological properties varied considerably. DOM1 treatment caused a marked decrease in soil pH compared to DOM2 treatment, which then led to the release of Ca 2+ and Mg 2+ and improved the solubility of inactive P. Moreover, DOM1 treatment was found to significantly raise the content of microbial biomass P (MBP), particularly at 60 days. The Mantel test and random forest analysis revealed that the strongest correlation was between MBP and available P. Furthermore, DOM1 treatment had a stimulating effect on the growth of phosphate‐solubilizing microorganisms, including Arthrobacter , Penicillium and Mortierella . This investigation could provide insights into how the chemodiversity of exogenous DOM affects the activation of legacy‐P in soil, thus enhancing the soil P supply capacity in agricultural systems.