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

Abstract

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. 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. 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. 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.