The potential for synthesized invasive plant biochar with hydroxyapatite to mitigate allelopathy of Solidago canadensis

Few studies tried to explore the mitigation effect and underlying mechanisms of biochar and their complex for negative allelopathy from invasive plants, which may provide a new way in the invasive plant management. Herein, an invasive plant (<em>Solidago canadensis</em>)-derived biochar (IBC) and its composite with hydroxyapatite (HAP/IBC) were synthesized by high temperature pyrolysis, and characterized by SEM, EDS, XRD, FTIR, and XPS. Then, both the batch adsorption and pot experiments were conducted to compare the removal effects of kaempferol-3-<em>O</em>-<em>β</em>-<em>D</em>-glucoside (C21H20O11, kaempf), an allelochemical from <em>S. canadensis, </em>on IBC and HAP/IBC, respectively. HAP/IBC showed a stronger affinity for kaempf than IBC due to its higher specific surface area, more functional groups (P-O, P-O-P, PO43-), stronger crystallization [Ca3(PO4)2]. The maximum kaempf adsorption capacity on HAP/IBC was 7 times higher than on IBC (10.482 mg/g &gt; 1.709 mg/g) via π-π interactions, functional groups, and metal complexation. The kaempf adsorption process could be fitted best by both pseudo-second-order kinetic and Langmuir isotherm models. Furthermore, HAP/IBC addition into soils could enhance and even recover the germination rate and/or seedling growth of tomato inhibited by negative allelopathy from the invasive<em> S. canadensis</em>. These results indicate that the composite of HAP/IBC could more effectively mitigate the allelopathy from <em>S. canadensis</em> than IBC, which may be a potential efficient approach to control the invasive plant and improve soils.