Genotype, Season and Temperature Steer the Fungal Communities Living on Norway Spruce Needles

The needles of Norway spruce carry a distinct community of fungi, and new field research shows that this phyllosphere mycobiome is shaped not only by the tree’s own genetic background but also, and to a greater degree, by the temperature conditions it experiences through the growing season. The study, led by Wenzi Ren and colleagues including Fred O. Asiegbu, examined seedlings classified as either partially resistant or susceptible to the fungal pathogen Heterobasidion.

The team sampled needles from both resistance classes growing in an open field in May, July and September of 2022, then characterized the fungal communities using internal transcribed spacer (ITS) amplicon sequencing. Three alpha-diversity measures, richness, diversity and evenness, all differed significantly between susceptible and partially resistant genotypes, with p-values below 0.05. The authors note that the distributions overlapped substantially between the two groups, meaning the differences were statistically clear but not absolute separators of individual trees.

Community composition told a more nuanced story. The fungal assemblages were associated with both host resistance phenotype and temperature-related variables, but average and accumulated temperature explained a greater proportion of the variation than resistance class itself. This suggests that seasonal thermal conditions act as a stronger filter on which fungi persist on spruce needles than the trees’ partial resistance status, although both factors leave a measurable imprint.

The researchers also compared the needle-inhabiting fungi with the seed-associated fungal communities of the same genotypes. The overlap was strikingly small: less than 1% of phyllosphere fungal taxa were shared with the seed communities, indicating that the needle mycobiome is largely assembled from sources other than the seed microbiome.

Network analyses added a final layer, revealing seasonal differences in fungal association patterns between partially resistant and susceptible seedlings. In other words, the web of co-occurring fungal taxa on the needles shifts across the season and does so differently depending on the host’s resistance background. The authors emphasize that the roles of host resistance phenotype, seasonal variation and accumulated temperature in shaping the spruce phyllosphere mycobiome had remained poorly understood, and this work provides field-based evidence that all three contribute, with temperature emerging as the dominant driver in their dataset.

Subject of Research: Factors shaping the phyllosphere fungal community of Norway spruce

Article Title: Host genotype, resistance status and seasonal temperature shape the Norway spruce phyllosphere mycobiome

Article References: Ren, W., Wen, Z., Wang, K., Azeez, A. A., & Asiegbu, F. O. (2026). Host genotype, resistance status and seasonal temperature shape the Norway spruce phyllosphere mycobiome. PLOS One, 21(10), e0360930. https://doi.org/10.1371/journal.pone.0360930

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0360930

Keywords: Norway spruce, phyllosphere, mycobiome, Heterobasidion, host resistance, seasonal variation, accumulated temperature, ITS amplicon sequencing, fungal ecology, seed microbiome, Host, genotype