Successive hexaconazole application altered the degradation behavior in soil and shifted microbial community and functional profiles

Abstract

High-frequency and high-dose application of the fungicide hexaconazole has caused the accumulated residues in agricultural soils. However, the degradation behaviors of hexaconazole and the ecological risks associated with its successive applications remain unknown. This study aimed to explore the degradation characteristics of hexaconazole in soil and its effects on soil microbial community structure and function under successive application conditions. The resulted showed that biodegradation was the primary pathway for hexaconazole degradation in soil. The degradation half-life (DT₅₀) of hexaconazole in soil were 18.7-67.3 days, initially increasing and then decreasing with successive applications. Higher concentration significantly prolonged the DT₅₀. Hexaconazole application significantly reduced soil microbial functional diversity as increasing treatment frequency. Successive applications altered the soil bacterial community composition and promoted the proliferation of 13 potential hexaconazole-degrading bacterial genera, including Methylibium and Variovorax. Moreover, these bacterial genera acted as biomarkers of hexaconazole treatment and were distributed in a same functional module in the bacterial network. While most soil microbial metabolic pathways were inhibited, a few, such as those related to cellular community-prokaryotes and cell motility, were stimulated. Notably, successive applications disrupted soil nitrogen cycling, especially suppressing the expression of key nitrification and denitrification genes, including AOA-amoA, AOB-amoA, and nirK. This study provides insights into the hexaconazole degradation in soil and highlights the ecological risks associated with its frequency application.

Keywords: Degradation characteristics; Hexaconazole; Microbial community and function; Soil nitrogen cycling; Successive application.