Effects of Corn Stover Biochar on Soil Bacterial and Fungal Biomarkers in Greenhouse Tomatoes Under Mulched Drip Irrigation

Although the role of biochar in enhancing soil quality has been extensively studied, its specific effects on the changes of soil bacteria and fungi in greenhouse tomato under mulched drip irrigation are not yet fully understood. In order to understand the above-mentioned changes, a two-year experiment on greenhouse tomatoes with mulched drip irrigation was conducted. The objective of this experiment was to explore the relationship between different irrigation levels (W1: 50–70% of the field capacity W2: 60–80% of the field capacity, and W3: 70–90% of the field capacity) and different biochar application rates (B0: 0 t/ha, B1: 15 t/ha, B2: 30 t/ha, B3: 45 t/ha, and B4: 60 t/ha) on soil bacteria and fungi. The results demonstrated that the soil bacterial Chao index was influenced by biochar application and water-biochar interactions, while the soil fungal α-diversity index and bacterial and fungal β-diversity were predominantly impacted by the irrigation level. The random forest modelling indicated that soil bacterial biomarkers were predominantly rare genera, while fungal biomarkers contained both dominant and rare genera. In comparison with the B0 treatment, biochar application resulted in an enhancement of the abundance of bacterial biomarkers associated with nutrient cycling, including Galbibacter (400.90–2216.22%) at the W3 levels. The B4 treatment at both W3 and W2 levels reduced the relative abundance of the pathogenic fungus Aspergillus sp., but the rest of the biochar treatments enhanced it by 4.69–108.16% and 55.86–213.30%, respectively. The Mantel test demonstrated that soil water content was the most significant influencing factor for all soil bacterial and fungal biomarkers. Biochar application significantly altered major bacterial biomarker functions in mulched drip irrigation, while fungal biomarker functions were mainly affected by irrigation levels and water-biochar interactions. At the W3 level, biochar application significantly reduced the relative abundance of Saprotroph–Symbiotroph by 83.44–97.92%. These results serve as a reminder of the critical importance of soil health sustainability in integrated crop management decisions and provide valuable insights for improving soil quality under mulched drip irrigation.