[Effects of Biochar Application on the Structure and Function of Fungal Community in Continuous Cropping Watermelon...

This study was conducted to clarify the long-term effects of biochar application on the structure and function of the fungal community in continuous cropping watermelon soil. Taking watermelon root soil as the research object, Illumina NovaSeq high-throughput sequencing and FUNGuild platform were used to analyze the differences in soil fungal community composition, diversity, and function after 3-year biochar additions of 7.5, 15.0, and 30.0 t·hm^-2 and to explore the correlation between soil environmental factors and fungal community structure under the control of biochar. The results showed that compared to that in the absence of biochar (control), the soil pH, available phosphorus, available potassium, total nitrogen, organic matter, and cation exchange capacity increased, but available nitrogen decreased with biochar addition. High-throughput sequencing results showed that biochar amendment improved the fungal community structure in continuous cropping watermelon soil and increased the richness and diversity of soil fungi. A total of 922 OTU were obtained from all soil samples, and the species annotation results indicated that the dominant fungal groups were Ascomycota, Basidiomycota, Mortierellomycota, Chytridiomycota, and Glomeromycota, with these phyla accounting for 85.70 %-92.45 % of the total sequences.The relative abundance of Ascomycota and Basidiomycota decreased, whereas the abundance of Mortierellomycota and Glomeromycota increased with biochar addition.At the genus level, the application of biochar increased the relative abundance of Mortierella and Rhizophlyctis but decreased the abundance of Fusarium. The Mantel test showed that soil available potassium, available nitrogen, organic matter, and pH were the main environmental factors leading to the shift in the soil fungal community composition.The functional prediction with FUNGuild showed that the many nutrient types among the different treatments were saprotrophic, pathotrophic, and symbiotrophic. The relative abundance of pathotrophs significantly decreased, but the abundance of symbiotrophs significantly increased with the medium and high doses of biochar treatment. In conclusion, the application of biochar changed the soil physicochemical properties, promoted the development of soil fungal community structure and functional groups in a healthy and beneficial direction, and improved the quality of continuous cropping watermelon soil.