Effects of oxytetracycline on plant growth, phosphorus uptake, and carboxylates in the rhizosheath of alfalfa

Aims: Residues of antibiotics such as oxytetracycline (OTC) in soil can affect microbial compositions and activities, thus affecting soil P availability, and consequently plant P uptake and growth. Methods: A pot experiment was performed to grow alfalfa in a loess soil with different doses of P (0, 25, 50, and 100 mg kg⁻¹) and OTC (0, 25, 50, and 100 mg kg⁻¹). Plant dry mass, shoot and root P concentrations, bulk soil and rhizosheath pH, rhizosheath carboxylates, and bulk soil alkaline phosphatase activity were determined. Results: Shoot dry mass and root dry mass increased with increasing P dose, while shoot dry mass decreased with increasing OTC dose, especially at lower P doses (0 and 25 mg kg⁻¹). Addition of OTC slightly reduced P concentrations in shoots and roots, but did not reduce plant P content consistently. Increasing OTC dose significantly reduced bulk soil alkaline phosphatase activity at 0P and strongly reduced rhizosheath tartrate amount at all P doses. Conclusions: The effects of OTC on plant growth and P uptake depended on both OTC and P doses in soil. High OTC dose had negative effects on shoot P uptake and growth, especially at lower P doses, while it had a positive effect on root growth at higher P doses.