[Biological Evaluation and Key Stress Factor Diagnosis of Compound Contaminated Soil Based on Environmental DNA]

Healthy biological community composition and diversity are the basis for soil ecosystems to provide complete ecological functions and services. The current technical bottleneck in soil pollution control is the lack of systematic and comprehensive biodiversity indicators. In this study, the compound-polluted soil in an industrial park was taken as the object, and environmental DNA (eDNA)technology was used to monitor and analyze the composition of the biological community in the polluted soil. The environmental DNA-species sensitivity distribution (eDNA-SSD) method was constructed to diagnose the key stress factors and their ecological threshold. The results showed that:① compound pollution did not have a significant impact on the α-diversity of soil organisms in the park but led to changes in the composition of biological communities and dominant species with high relative abundance. The dominant groups in the polluted soil were Proteobacteria (25.54%), Ascomycota (15.65%), Actinobacteria (8.75%), and Chloroflexi (7.64%). ② Environmental factors accounted for 51.27% of the differences in soil biodistribution, and aniline, sulfate, petroleum hydrocarbon, and lead were the key stress factors for soil biomes. Among them, aniline had the most significant effect on the community distribution of bacteria (P=0.030), sulfate on fungi (P=0.025), and metazoans (P=0.032). ③ The ecological risk threshold (hazardous concentration for 5% of species, HC₅) of pollutants with 95% species as the protection target showed a gradient decreasing trend of sulfate (470.00 mg·kg^-1), petroleum hydrocarbon (17.00 mg·kg^-1), lead (13.00 mg·kg^-1), arsenic (6.20 mg·kg^-1), 4-chloroaniline (0.16 mg·kg^-1), and aniline (0.11 mg·kg^-1). Nevertheless, the existing soil risk control value was significantly higher than the ecological risk value, indicating that the existing control standards targeting human health were not suitable for protecting soil health. The comprehensive pollution index showed that the soil pollution in the park was mostly mild pollution accompanied by heavy pollution at individual points. The biological evaluation method based on eDNA-SSD could achieve the comprehensive evaluation of composite pollution in the absence of the benchmark value of pollutants and at the same time better distinguish the differences in soil biological community structure and composition under different pollution levels (P=0.053). In conclusion, the environmental DNA soil biomonitoring and assessment method developed in this study has guiding significance and application value for soil ecosystem restoration assessment.