Abstract: As a commonly used herbicide in maize fields, the soil residue accumulation of nicosulfuron can inhibit maize seedling development and cause phytotoxicity to susceptible following plants. This study aims to investigate the remediation capacity and mechanism of the nicosulfuron-degrading bacterium Klebsiella jilinsis 2N3 on contaminated soil. Under the stress condition of 8 mg/kg nicosulfuron, the growth of maize seedlings was significantly inhibited, with the maximum reduction in stem and leaf dry weight reaching 75.11%. Inoculation of strain 2N3 achieved a 66.02% nicosulfuron degradation efficiency after 28 days of treatment. GFP labeling assays revealed that the root colonization population of strain 2N3 decreased from an initial density of 1×10⁸ CFU/g to 8.51×10⁴ CFU/g at 21 days post-inoculation. Pot bioassays using rapeseed and cucumber as susceptible plants revealed that strain 2N3 significantly restored the growth of both vegetables compared to the 1 mg/kg nicosulfuron control. Plant height, root length and shoot fresh weight of rapeseed increased by 26.70%, 51.94% and 34.89%, whereas those of cucumber increased by 13.95%, 7.86% and 9.96%, respectively. Furthermore, strain 2N3 enhanced leaf SOD and POD activities, lowered MDA levels, and promoted root activity in both vegetables. These findings verify that strain 2N3 is capable of degrading nicosulfuron in soil and mitigates herbicide phytotoxicity in sensitive vegetable crops.

Key words: nicosulfuron, degradation bacteria 2N3, rhizosphere colonization, susceptible plant, microbial bioremediation