Influences of plants and soil microbes on antibiotics in the rhizosphere: a review

The rhizosphere plays an important role in both farmland and urban areas, affecting water quantity and quality during surface water infiltration by increasing the heterogeneity of the aeration zone. The extensive application of antibiotics, their recalcitrance to degradation, and the resultant accumulation of antibiotics in soil-microbe-plant systems represent significant threats to the rhizosphere system, thereby threatening ecological stability and environmental and human health. This review synthesises recent findings on the migration and transformation of typical and common antibiotics within the rhizosphere. The main findings include that the absorption of antibiotics by plants is influenced by their molecular weight (MW) and octanol-water partition coefficient (log Kow), allowing antibiotics to be divided into three classes: (1) antibiotics with high lipophilicity (log Kow > 2) are mostly adsorbed by root lipids and rarely participate in the soil-plant transport process; (2) antibiotics with log Kow < 2 and high MWs (MW > 700) are blocked outside the plant roots; and (3) antibiotics with log Kow < 2 and low MWs (MW < 700) can enter plants through the roots and are transported via transpiration flow in plants. Antibiotics with log Kow < 1 are more easily transported into plant tissues, including leaves. The rhizospheric microorganisms capable of participating in antibiotic migration and transformation are concentrated in Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes. The inhibitory effect of antibiotics on dehydrogenase, sucrase, urease, catalase, and alkaline phosphatase activities surpasses their promoting effect, reducing these enzyme activities by 6-35% on average. However, the promoting effect of antibiotics on peroxidase, acidic phosphatase, and manganese peroxidase outweighs the inhibitory effect, increasing enzyme activity by 2-23%. Furthermore, it is essential to consider the effects of plant age and root characteristics on antibiotic migration and transformation. The results of this review contribute to a better understanding of the migration and transformation of antibiotics within the rhizosphere.