Short-term response of soil enzyme activities and bacterial communities in black soil to a herbicide mixture: Atrazine and Acetochlor

Combined application of atrazine (ATZ) and acetochlor (ACE) was used as an emerging herbicidal method in black soil zone of northeastern China recently. However, the interaction toxic effect of the two herbicides on the soil biological characteristics has not been investigated yet. In this study, the alterations of soil enzyme activities and bacterial communities in black soil were assayed during a short term (28 days) exposure period by spiking ATZ, ACE or ATZ + ACE (1:1, w: w) at 0×, 1×, 2×, 5× and 10× the recommended dose in a microcosm experiment conducted under greenhouse condition. The results showed that ATZ and ACE had synergistic inhibitory effects on soil enzymes activities. Higher inhibition rates of urease, acid phosphatase, sucrase and catalase were observed in ATZ + ACE, and the enzyme activities could not recover to the level without herbicide application after 28 days. The higher IBRv2 value of ATZ + ACE also indicated that the comprehensive toxicity was stronger than that of ATZ or ACE. The microbial community structure was affected differently by ATZ, ACE and ATZ + ACE as the PLFAs analysis displayed, and ATZ + ACE was more harmful to bacteria than ATZ or ACE. The decrease in relative abundance of Proteobacteria was more sensitive to ATZ, and the decrease of Acidobacteriota was more sensitive to ACE, and the relative abundance of these two phyla decreased more obviously in ATZ + ACE. In addition, the PICRUSt analysis showed that the functions of the replication and repair, energy metabolism, cell motility and cellular processes and signaling were inhibited by ATZ and ACE, especially in the ATZ + ACE treatment. This means that combined application of ATZ and ACE has a greater potential risk on soil microbes and consequently the nutrient cycling process.