Effects of biochar and Trichoderma on bacterial community diversity in continuous cropping soil

Soil acidification has become a serious issue in protected production in northern China as a consequence of many years of continuous cropping. Besides affecting the growth and quality of vegetables, soil acidification also restricts the sustainable development of vegetables grown in protected environments. A single application of biochar or Trichoderma can repair the soil environment, optimize the microbial community structure, reduce plant diseases, and promote plant growth. However, it is not known whether biochar combined with Trichoderma has a synergistic effect on these parameters. In this study, long-term continuous cropping of cucumbers in a greenhouse was used to study the effect of biochar and Trichoderma on micro-ecological environmental changes in acidified soil using Illumina sequencing. The results showed that the combined application of biochar and Trichoderma promoted cucumber growth; significantly enhanced root vitality and superoxide dismutase, peroxidase, and catalase activities in leaves; and reduced malondialdehyde content. In addition, soil physical and chemical properties improved; cation exchange capacity, the activity of soil polyphenol oxidase and invertase, and the diversity of soil bacterial communities increased; and the structure and relative abundance of soil bacteria changed after the combined application of biochar and Trichoderma. Correlation analysis of environmental factors showed that total nitrogen and soil pH had the greatest impact on bacterial communities. The metabolic function of soil bacteria was improved, and the circulation of soil nutrients was increased as a consequence of the combined application of biochar and Trichoderma.