Interannual dynamics of Tuber melanosporum and fungal communities in productive black truffle orchards amended with truffle nests

Truffle nests did not increase black truffle mycelial growth, but generated a less diverse fungal community, acting as an open niche for fungal colonization and seemingly alleviating ectomycorrhizal competition. Truffle growers devote great efforts to improve black truffle productivity, developing agronomic practices such as 'truffle nests' (peat amendments that are supplemented with truffle spore inoculum). It has been hypothesized that improved fruiting associated with nests is linked to stimulation of truffle mycelia previously established in soil or to changes generated in soil fungal community. To assess this, we used real-time PCR to quantify black truffle extraradical mycelium during 2 years after nests installation. We also characterized the fungal community via high-throughput amplicon sequencing of the ITS region of rRNA genes. We found that neither the abundance of truffle mycelium in nests nor in the soil-nest interphase was higher than in the bulk soil, which indicates that nests do not improve mycelial growth. The fungal community in nests showed lower richness and Shannon index and was compositionally different from that of soil, which suggests that nests may act as an open niche for fungal colonization that facilitates truffle fruiting. The ectomycorrhizal fungal community showed lower richness in nests. However, no negative relationships between amount of truffle mycelium and reads of other ectomycorrhizal fungi were found, thus countering the hypothesis that ectomycorrhizal competition plays a role in the nest effect.

Automated summary

The study found that truffle nests did not promote the growth of black truffle mycelium, but led to a less diverse fungal community. The nests acted as an open niche for fungal colonization and helped alleviate ectomycorrhizal competition. Contrary to the hypothesis, the nests did not improve mycelial growth or negatively affect the abundance of other ectomycorrhizal fungi, suggesting that ectomycorrhizal competition does not play a role in the nest effect.