Rhizosphere response of Phragmites communis to the exposure of propranolol: root morphology, soil carbon fraction, and microorganism

Propranolol (PRO) has been detected in water bodies worldwide, attributed to the incomplete removal by wastewater treatment processes. Although reports exist on the removal of PRO by wetland plants such as Phragmites communis, research on the impact of PRO on SOC fractions in plant rhizospheres remains scarce. This investigation examined the impacts of various concentrations of PRO on the rhizosphere of Phragmites communis over a 21-day laboratory experiment. As PRO concentration increased, a notable decrease in SOC content was observed: specifically, the proportion of mineral-associated organic carbon (MAOC) rose (from 47.90% to 33.17%), whereas the proportion of particulate organic carbon (POC) significantly declined following PRO treatment (from 52.10% to 66.83%). PRO exposure moderately promoted root growth, notably enhancing fine root development at lower concentration, although it significantly inhibited root respiration. Despite the overall bacterial community showing no significant alteration with PRO exposure, specific carbon-cycling phyla experienced significant promotion or inhibition, principally among Bacteroidetes, Proteobacteria, Verrucomicrobia, and Nitrospirae. Metabolomic analysis demonstrated that rhizosphere-associated bacteria, such as Curvibacter, Chitinophaga, and Algoriphagus, influenced SOC fractions predominantly through altering the synthesis of organic and fatty acids upon PRO exposure. Additionally, across varying PRO concentrations, plant influence emerged as the predominant factor affecting POC alterations, whereas MAOC changes resulted from the synergistic interaction of plants and associated bacteria.