Cross-scale mechanisms and molecular-ecological thresholds of phthalate stress in the cucumber-soil system

Phthalates (PAEs) are widespread soil contaminants that threaten the sustainability of agricultural lands, yet the threshold mechanism by which they trigger collapse of the cucumber-soil system remains unclear. Integrating physiological, ultrastructural, proteomic, and microbiome analyses, this study tracked the dose-response of the cucumber-soil system to PAEs (0, 5, and 15 mg/kg). A biphasic response was identified: 5 mg/kg induced "reversible compensation," where upregulated antioxidant enzymes and proline preserved physiological function and high rhizosphere bacterial diversity. Conversely, 15 mg/kg triggered "irreversible collapse." Proteomics and pathway modeling revealed the core mechanism: despite a burst in GST synthesis, the failure of the ASA-GSH regeneration cycle caused a redox collapse (GSH/GSSG ≈ 0.02) and subsequent organelle disintegration. Concurrently, the rhizosphere microbiome underwent structural simplification, shifting from a complex cooperative network to one dominated by tolerant taxa (Bacillus, Sphingomonas). By identifying the topological flip from protective to destructive regulation, this study establishes a cross-scale "molecular-ecological" threshold framework, providing a quantifiable scientific basis for hierarchical risk management in PAEs-contaminated farmland.