PurposeBiochar has been proven to mitigate the detrimental impacts on the high use of nitrogen (N) fertilizer on vegetable yield by influencing the microbial community, but the impacts on the microbial pathway of biochar remain unclear.MethodsA pot experiment of pakchoi was conducted with eight treatments, including normal level (100 mg N kg-1: N1) and high level (200 mg N kg-1: N2) of N fertilizer treatments, as well as four biochar levels (0%: B0, 0.5% w/w: B05, 1% w/w: B1, and 2% w/w: B2) to determine its practical effects.ResultsHigh nitrogen fertilizer significantly reduced pakchoi yield. Biochar increased the pakchoi yield by 13.46-55.76% at N1 and 53.3-75.56% at N2, but the effect of the application of biochar on pakchoi yield rates was not significant. The bacterial and fungal diversity was significantly increased by biochar but was decreased by high N in vegetable soil. Soil bacterial communities were dominated by Proteobacteria, Actinobacteriota, Gemmatimonadota, Acidobacteriota, and Chloroflexi, while soil fungal communities were dominated by Ascomycota, Chytridiomycota, Mortierellomycota, and Basidiomycota. Biochar and nitrogen fertilizer all changed the bacterial and fungal community composition.ConclusionsBiochar enhanced the pakchoi yield through regulated bacterial communities, but the regulatory pathways vary under different N levels. It enhanced the prevalence of beneficial species involved in disease suppression and supported the soil organic matter degradation, thereby resulting in increased vegetable yield at N1. It increased the abundance of eutrophic species, which were related to the available nutrients in the soil and its retention capacity to improve the yield at N2. It was noteworthy that biochar could increase the risk of vegetable yield reduction by reduction of nutrient cycling phylum and enhancement of soil-borne plant pathogens at a higher nitrogen level.
