Differential Selection Effects of Continuous AITC Fumigation on Soil Microbial Communities and Functions and Identification of Tolerant Strains

Allyl isothiocyanate (AITC) is effective as a bio-based fumigant in controlling soil-borne diseases; however, the selective pressure it exerts on soil microecology and evolutionary dynamics remains inadequately characterized. This study systematically investigated the remodeling effects of continuous AITC fumigation on soil microbial communities, functional genes, and functional strains by integrating metagenomic analysis and pure culture techniques. Results demonstrate that AITC drives directional selection from “sensitive” to “tolerant” microorganisms. Fungal communities exhibit greater cumulative damage than bacterial communities, with the proportion of significantly suppressed fungi increasing linearly from 9.3% at baseline to 35.7%. At the genus level, sensitive groups were predominantly enriched in pathogen-associated genera, e.g., Pseudomonas and Xanthomonas, whereas tolerant groups, represented by Bacillus and Streptomyces, maintained ecological dominance under continuous stress. Functionally, AITC induced differential evolution of functional gene repertoires. Nitrogen cycle genes (e.g., amoC) exhibited high negative sensitivity, with significant downregulation by 20%, whereas the TCA core module in the carbon cycle exhibited strong robustness. Virulence assays confirmed EC50 values for tolerant beneficial bacteria (Bacillus spp.) (>40 mg·L−1) were significantly higher than those for pathogens (1.3–7.9 mg/L). This study established a microbial “sensitive-tolerant” response framework under AITC stress, revealing the core potential of endogenous tolerant strains for the precise ecological restoration of fumigated soils.