Elevated CO₂ promotes the translocation and degradation of strobilurin fungicides in cucumber via coupled physiological and metabolic pathways.

Elevated atmospheric CO₂ is a prominent consequence of global climate change, which substantially alters plant physiological processes and further modulates the environmental fate of pesticides in agricultural ecosystems, thereby threatening agricultural product safety and ecological health. Nevertheless, the physiological and biochemical mechanisms underlying elevated CO₂-regulated uptake, translocation, and metabolism of fungicides in crop plants remain largely unclear. In the present study, cucumber seedlings were selected as the model plant, and integrated physiological detection, subcellular distribution analysis and untargeted metabolomics were adopted to explore the responses of three typical strobilurin fungicides (azoxystrobin, pyraclostrobin, and trifloxystrobin) to ambient and elevated CO₂ levels (700 and 1100 μmol/mol). Results showed that moderate CO₂ enrichment (700 μmol/mol) distinctly facilitated upward acropetal translocation of azoxystrobin and pyraclostrobin, which was driven by increased stomatal conductance and transpiration force, together with higher soluble fraction proportion at subcellular level. By contrast, highly lipophilic trifloxystrobin was mainly retained in roots, exhibiting only limited and inefficient upward translocation, and its translocation behavior was insensitive to variations in CO₂ concentration. Moreover, elevated CO₂ markedly accelerated leaf degradation of all tested fungicides, reducing their half-lives by 32%-65% under 700 μmol/mol. Such accelerated degradation was closely associated with enhanced glutathione S-transferase activity. Metabolomic analysis further revealed remarkable alterations in glutathione metabolism and phenylpropanoid biosynthesis, demonstrating activated plant detoxification defense systems. Overall, this study clarifies the mechanistic links between atmospheric CO₂ elevation and fungicide dynamics in crops, providing fundamental references for pesticide risk assessment under future climate scenarios.