Sod Culture with Vicia villosa Alters the Diversity of Fungal Communities in Walnut Orchards for Sustainability Development

Monoculture frequently causes loss of soil nutrients and the emergence of soil-borne diseases in walnut orchards, whereas it is unknown whether sod culture with Vicia villosa (a popular agroforestry system) in walnut orchards impacts the structural composition and diversity of soil fungal communities. Fungal communities in walnut orchards with the cover plant V. villosa were investigated in this work utilizing high-throughput sequencing of ITS, as well as examination of root arbuscular mycorrhizal colonization and hyphal length of soil fungi. The monoculture and interplanted walnut models generated 33,511 and 34,620 effective tags with sequence similarity of 97%, respectively annotating 245 and 236 operational taxonomic units (OTUs). Among these, a total of 158 OTUs were found to be shared across monoculture and interplanted orchards. Walnuts grown in monoculture had a total of 245 species, belonging to 245 genera and 36 phyla, while walnuts with V. villosa as cover crops had 236 species, belonging to 236 genera and 19 phyla. The application of V. villosa as a cover plant significantly increased 1-Simpson and Shannon indices of soil fungi, indicating that interplanting V. villosa promoted soil fungal community diversity. Three dominant fungal phyla were detected in the soil, with Glosseromycota being the most dominant phylum. V. villosa as a cover plant significantly reduced the abundance of Funneliformis and Densospora in the soil, while it significantly increased the colonization of native arbuscular mycorrhizal fungi in roots by 94%, along with a 39% significant decrease in mycorrhizal hyphal length, as compared with the monoculture. Overall, V. villosa as a cover plant alters the composition and diversity of the soil fungal community, with reduced Funneliformis (F. geosporum) and Densospora abundance, and increased mycorrhizal colonization rate in roots, contributing to the sustainable and high-quality development of walnuts.