Fungal Community Composition and Diversity Across Soil Depths Under Different Cover Crop Treatments

Fungi are a critical component of microbial biomass in agricultural soils, but their distribution across soil depths under different cover crops remains poorly understood. We used high-throughput sequencing of fungal ITS1 amplicons to characterize fungal communities across four soils depths (0–2, 2–4, 4–10, and 10–20 cm) in experimental field plots under four cover crop treatments: winter fallow reference (REF), cereal rye (CRYE), wild pennycress (WPEN), and a mixture of pea, crimson clover, radish, and oat (PCRO). There was no significant interaction between soil depth and cover crop treatment on both alpha diversity and beta diversity. CRYE and PCRO cover crops had low abundance of Fusarium, a genus including many important plant pathogens, and different fungal community composition relative to REF. Fungal diversity was significantly higher at 4–10 cm compared to 0–2 cm depth, but fungal richness was not affected by soil depth. Fungal community composition differed significantly between 0–4 and 10–20 cm soil depths. The relative abundance of Mortierella and unclassified Basidiomycota increased with increasing soil depth while that of Calvatia, Cryptococcus, Fusarium, and Idriella decreased with increasing soil depth. Most fungal taxa were assigned to more than one guild, but the few taxa that were classified as strict saprophytes decreased with increasing soil depth while those classified as strict symbionts increased with increasing soil depth. These differences were associated with low pH and high content of OM, K, S, P, and Zn in the topsoil layer compared to the deeper soil layer. The findings may inform the development of targeted soil management practices to promote beneficial fungi, but additional studies covering multiple study sites and sampling dates are needed for clarity.