Local Tree Diversity Suppresses Foliar Fungal Infestation and Decreases Morphological but Not Molecular Richness in a Young Subtropical Forest

Abstract

Leaf fungal pathogens alter their host species’ performance and, thus, changes in fungal species composition can translate into effects at the tree community scale. Conversely, the functional diversity of tree species in a host tree’s local neighbourhood can affect the host’s foliar fungal infestation. Therefore, understanding the factors that affect fungal infestations is important to advance our understanding of biodiversity-ecosystem functioning (BEF) relationships. Here we make use of the largest BEF tree experiment worldwide, the BEF-China experiment, where we selected tree host species with different neighbour species. Identifying fungal taxa by microscopy and by high-throughput DNA sequencing techniques based on the internal transcribed spacer (ITS) rDNA region, we analysed the fungal richness and infestation rates of our target trees as a function of local species richness. Based on the visual microscopic assessment, we found that a higher tree diversity reduced fungal richness and host-specific fungal infestation in the host’s local neighbourhood, while molecular fungal richness was unaffected. This diversity effect was mainly explained by the decrease in host proportion. Thus, the dilution of host species in the local neighbourhood was the primary mechanism in reducing the fungal disease severity. Overall, our study suggests that diverse forests will suffer less from foliar fungal diseases compared to those with lower diversity.

Foliar Fungal Endophytes in a Tree Diversity Experiment Are Driven by the Identity but Not the Diversity of Tree Species

“…Our main findings, however, confirmed neither the published positive [15] or negative effects of tree diversity on FEF diversity [17]. Such an inconsistency in host-endophyte diversity relationships has also been reported from samples of Norway spruce in mature forests [38] and from the largest subtropical tree diversity experiment in China [18].…”

“…In a three-year-old and more sparsely planted experiment in the US, Griffin et al [17] found the opposite relationship. In the largest tree diversity experiment in China, Saadani et al [18] found that foliar fungi in general (including endophytic and pathogenic species) were not affected by the diversity of the tree neighborhood. Tentatively, one might speculate that the effects of tree diversity on FEF might increase with the age and the density of the planted trees.…”

Effects of enemy exclusion on biodiversity–productivity relationships in a subtropical forest experiment

“…and in nearby natural forest stands (Brezzi et al, 2017). In contrast, foliar fungal infestation in the experiment was suppressed by tree diversity (Saadani et al, 2021). Taken together, these observations suggest that leaf fungi benefited from higher host densities in monoculture, and their suppression therefore led to increased productivity at low diversity and a weakened species-richness effect at the community-level.…”

“…Similar positive effects of tree species richness on herbivores and herbivory were observed in the additional plots of the BEF‐China experiment referred to above (Schuldt et al, 2017), in plots with a higher genetic diversity within species (Hahn et al, 2017), and in nearby natural forest stands (Brezzi et al, 2017). In contrast, foliar fungal infestation in the experiment was suppressed by tree diversity (Saadani et al, 2021). Taken together, these observations suggest that leaf fungi benefited from higher host densities in monoculture, and their suppression therefore led to increased productivity at low diversity and a weakened species‐richness effect at the community‐level.…”