Remediation of acetochlor-contaminated maize field soil using Serratia odorifera AC-1 fertilizer: effects on soil microbial communities

Abstract

Acetochlor is a chloroacetamide herbicide that is widely applied in corn fields. Nevertheless, the long-term usage of acetochlor in the soil leads to residues, which severely affect the germination of corn seeds and the growth of seedlings, and even exert an influence on the soil microbial community. Microbial degradation of acetochlor is the principal approach for restoring the soil microbial ecology. In this study, the Serratia odorifera AC-1 strain was isolated and identified from the soil for the degradation of residual acetochlor in the soil. To enhance the degradation efficiency, a solid microbial agent was prepared by using activated carbon as a carrier and the AC-1 strain at a 1:1 ratio and applied to the soil for degradation and remediation experiments. The content of the microbial cells in the solid microbial agent was 1.49 × 106 CFU/g after 120 days of preparation. The application of the AC-1 solid microbial agent significantly influenced the relative abundance of soil microbial communities (Actinobacteria, Firmicutes, and Proteobacteria), increasing the diversity of bacterial populations in the soil. The experimental results indicated that after the application of the AC-1 solid microbial agent, the plant height, stem diameter, and photosynthetic efficiency of corn seedlings under acetochlor stress were significantly elevated. When the application rate of the AC-1 solid microbial agent was 5.00 mg/kg, the stem diameter of corn increased by 56.4% compared with the control group. When the acetochlor concentration in the soil was 6.65 mg/kg, the DT50 value of the AC-1 solid microbial agent was 2.28 days. This study clarified the degradation mechanism and remediation capacity of the Serratia odorifera AC-1 strain in acetochlor-contaminated soil and proposed a new strategy to improve the stability and degradation efficiency of the microbial strain by optimizing the immobilization technology of the strain on activated carbon. This research provides a scientific basis and technical guidance for the future application of bioremediation technology in the field environment to remove pesticide residues, restore soil health, and enhance crop productivity.

Keywords: Serratia odorifera; acetochlor; bioremediation; seed germination; soil microbial communities.

Figure 1

Analysis of the influence of the ratio of fermentation broth and bacterial suspension to activated carbon on cell activity of Serratia odorifera AC-1. (A) Growth curves of AC-1 fermentation broth and bacterial suspension; (B) Effects of different ratios of AC-1 fermentation broth and AC-1 bacterial suspension on cell activity; (C) Effects of different ratios of AC-1 bacterial suspension and activated carbon on cell activity; (D) Effects of activated carbon fixation on cell activity of AC-1 fermentation broth and bacterial suspension.

Figure 2

Effects of different application rates of AC-1 solid inoculant on the degradation dynamics of acetochlor and the growth of corn seedlings and plants. (A) Effect of AC-1 solid inoculant application rate on the degradation dynamics of acetochlor at a concentration of 6.65 mg/kg; (B) Effect of AC-1 solid inoculant application rate on the degradation dynamics of acetochlor at a concentration of 3.34 mg/kg; (C) Effect of AC-1 solid inoculant application rate on the degradation dynamics of acetochlor at a concentration of 2.66 mg/kg; (D) Effect of different application rates of AC-1 solid inoculant on the growth of corn seedlings; (E) Effect of different application rates of AC-1 solid inoculant on the growth of corn plants.

Figure 3

Measurement of growth indicators in corn seedlings. (A) stem diameter trends of corn seedlings; (B) plant height trends of corn seedlings; (C) differences in photosynthetic efficiency of corn seedlings; (D) differences in chlorophyll content of corn seedlings. *AC-31 (low concentration), AC-32 (medium concentration), AC-33 (high concentration): Used to study the effects of different concentrations of AC-1 solid microbial agent in remediating acetochlor-contaminated soil; BCK3: Treatment group using only the AC-1 solid microbial agent without adding acetochlor, serving as a baseline to observe the individual effects of AC-1 on plants; ACK3: Treatment group using only acetochlor contaminated soil to evaluate the impact of acetochlor on plant growth.

Figure 4

Analysis of the Effects of AC-1 solid microbial agent on soil microbial diversity and AC-1 degradation pathways: (A) Heatmap of soil diversity analysis; (B) Functional abundance markers of Serratia odorifera AC-1 degradation pathways.

Figure 5

Relative abundance of microorganisms in acetochachlorine-contaminated soil caused by AC-1 degrading bacteria: CK was the abundance of microbial species in the original soil; AC09: Microbial species abundance in soil with acetochlor content of 6.65 mg/kg; AC-1: 5.0 mg/kg bioorganic fertilizer was added to acetochlor contaminated soil.