Acid compost tea (CT) is an acidic liquid organic fertilizer, which can be used for topdressing throughout the period of cotton growth in drip irrigation cotton fields with calcareous soil. However, its effects on soil bacteria and cotton roots are not clear. This study investigated the response of cotton roots and rhizosphere bacteria to CT application. Compared with organic fertilizer, the total root length, surface area, and volume were found to increase by 18.9%, 19.9%, and 20.7% upon CT treatment, respectively. However, the abundance of rhizosphere bacteria decreased upon CT treatment. The relative abundance of bacteria associated with root growth and rhizosphere environmental health, such as Micrococcaceae, Nocardioidaceae, and Sphingomonadaceae, increased significantly, whereas the relative abundance of oligotrophic bacteria, such as Methylmirabilota, decreased. Random forest distribution showed that the cotton root was the main factor affecting rhizosphere bacterial abundance and diversity, while soil properties (pH, total nitrogen, and organic carbon) and roots affect the relative abundance of some species together. The gene expression associated with metabolism, environmental adaptation, and immune system in rhizosphere bacteria increased. In conclusion, CT can improve soil properties and promote the growth of cotton roots, and cotton roots in turn exert regulatory effects to promote the growth of beneficial bacteria in the rhizosphere and affect their functions. CT has considerable application potential for the sustainable development of cotton fields with calcareous soil.

酸性堆肥茶（CT）是一种酸性液体有机肥，可用于钙质土壤滴灌棉田的棉花生长期追肥。但其对土壤细菌和棉花根系的影响尚不清楚。本研究调查了棉花根和根际细菌对 CT 应用的反应。与有机肥相比，CT处理后总根长、表面积和体积分别增加了18.9%、19.9%和20.7%。然而，CT处理后根际细菌的丰度降低。与根系生长和根际环境健康相关的细菌的相对丰度，如微球菌科、诺卡氏菌科和鞘氨醇单胞菌科, 显着增加, 而贫营养菌的相对丰度, 如Methylmirabilota, 减少。随机森林分布表明，棉花根系是影响根际细菌丰度和多样性的主要因素，而土壤性质（pH、总氮和有机碳）和根系共同影响某些物种的相对丰度。根际细菌中与代谢、环境适应和免疫系统相关的基因表达增加。综上所述，CT可以改善土壤性质，促进棉花根系的生长，而棉花根系反过来发挥调节作用，促进根际有益菌的生长，影响其功能。CT对钙质土壤棉田的可持续发展具有相当大的应用潜力。