Impact of Fluxapyroxad and Mefentrifluconazole on Microbial Succession and Metabolic Regulation in Rice Under Field Conditions

This study systematically evaluated the residual behavior of fluxapyroxad (FXP) and mefentrifluconazole (MFZ) in rice-soil systems, alongside their soil and metabolic impacts. Analytical methods validated via linear regression (0.0001-0.05 mg/L) complied with EU guidelines, demonstrating recoveries of 71.97-114.96%, RSDs ≤ 12.12%, and effective mitigation of matrix effects (-85.08% to -76.97%) using matrix-matched calibration. Residual dissipation followed first-order kinetics, with half-lives (T_1/2) spanning 10.83-21.00 d (FXP) and 23.10-57.76 d (MFZ). Notably, MFZ exhibited prolonged persistence in brown rice (T_1/2 = 57.76 d), though final residues (0.031 ± 0.001 μg/g FXP; 0.011 ± 0.0003 μg/g MFZ) remained below regulatory limits (China: 1 mg/kg; CAC: 5 mg/kg). Microbial analysis revealed transient diversity loss in rhizosphere communities (Chao1 index, <i>p</i> < 0.05), recovering by 21 d, while endophytes displayed resilience linked to plant metabolites. Enrichment of degraders (e.g., <i>Sphingomonas</i>) contrasted with suppression of nitrogen-fixing <i>Bradyrhizobium</i>, indicating functional trade-offs. Metabolomic profiling identified 3512 metabolites, with 332 and 173 differentially expressed metabolites at 7 d (S) and 21 d (T), dominated by lipids, benzenoids, and phenylpropanoids. Key metabolic shifts included a 2.11-fold increase in coumarin and elevated L-aspartic acid, highlighting adaptive responses via phenylalanine and TCA cycle pathways. Correlation analyses linked stress-tolerant endophytes (<i>Azorhizobium</i>) to defense-related metabolites (e.g., coumarin), suggesting microbial modulation of plant resilience. These findings emphasize the need for integrated strategies combining residue monitoring, microbial management, and metabolic insights to mitigate agrochemical risks in sustainable agriculture.