Reducing residues of tetracycline and its resistance genes in soil-maize system and improving plant growth: Selecting the best remediation substance

Tetracycline (TC) and tetracycline resistance genes (TRGs) in plant edible tissues pose a potential risk to the environment and then to human health. This study used a pot experiment to investigate the effects of different remediation substances (worm castings, fungal chaff, microbial inoculum, and biochar) on the physiological characteristics of maize and the residues of TC and TRGs in the soil-maize system under TC stress. The results showed that TC significantly inhibited growth, disrupted the antioxidant defense system balance, and increased proline and malondialdehyde contents of maize plants. Tetracycline residue contents were significantly higher in root than in shoot, and followed the order root > stem-leaf > grain, which was consistent with the distribution of bioconcentration factors in the different organs of maize plants. The TC residue content in the soil under different treatments was 0.013–1.341 mg kg-1. The relative abundances of different antibiotic resistance genes in the soil-maize system varied greatly, and in maize plants followed the order intI1 > tetW > tetG > tetB > tetM > tetX > tetO. In the soil, tetX had the highest relative abundance, followed by tetG and tetW. A redundancy analysis (RDA) showed that TC was positively correlated with TRGs. The addition of different remediation substances alleviated the toxicity of TC on maize physiological characteristics and reduced the TC and TRG residues in the soil-maize system, with biochar being the best remediation substance. These results provide new insights into the effect of biochar on the migration of TC and TRGs from soil to plants.