Exploring variation in phyllosphere microbial communities across four hemlock species

Abstract

The hemlock woolly adelgid (HWA) is an insect native to Asia and likely western North America. First reported in eastern North America in 1951, it has devastated eastern hemlock (Tsuga canadensis) populations. Loss of hemlock will greatly affect the structure and function of eastern forests. Susceptibility to adelgid infestation varies within eastern hemlocks and across other hemlock species. Our study was conducted to determine whether eastern hemlocks share a similar stem (phyllosphere) microbial community with other co‐occurring hemlocks and whether community‐level shifts are associated within trees of the same species based on HWA infestation. Surprisingly, we found no difference in microbial community composition or diversity between trees of the same species based on the level of HWA infestation. However, microbial communities varied significantly across the four hemlock trees sampled, native T. canadensis and three non‐natives: Tsuga chinensis, Tsuga dumosa, and Tsuga sieboldii. Within these tree hosts, microbial communities from T. dumosa and T. chinensis clustered together, and microbial communities from T. canadensis and T. sieboldii clustered separately from all other tree species. Additionally, specific indicator taxa were identified for all the tree species sampled. These results indicate that Asian hemlocks might not fill the same niche in eastern forests as the native eastern hemlock. Further work should be conducted to determine how differences in hemlock species and associated microbial communities might scale up to alter organismal interactions involving hemlocks.

Microbiome Variation Across Two Hemlock Species With Hemlock Woolly Adelgid Infestation

“…Because the relative dominance of mycorrhizal types can potentially affect ecosystem-level processes (Phillips et al, 2013), the impact of HWA infestation on co-occurrence of AM and EM fungi in hemlock warrants detailed research. Consistent with earlier work (Rogers et al, 2018), we found a greater percent of the variation in the microbiome composition explained by host species than by HWA population level. The effect of host species on the microbiome composition was strongest in the needles, branches, and roots, where the plant has a relatively stronger control over the microbiome environment (Kembel et al, 2014).…”

“…These broad taxonomic patterns among different plant-associated habitats resemble those found in other temperate tree species such as Magnolia kwangtungensis (Qian et al, 2019), Populus trichocarpa and P. deltoides × P. trichocarpa hybrids (Cregger et al, 2018), and Picea abies (Kovalchuk et al, 2018;Ren et al, 2019;Terhonen et al, 2019), suggesting that, at higher taxonomic levels, microbiomes are fairly consistent among tree species. However, as our study and others show, at more specific taxonomic levels, microbiomes diverge among closely related host species (Cregger et al, 2018;Rogers et al, 2018) and even among different genotypes of the same host species (Bálint et al, 2013;Veach et al, 2019).…”

“…Tsuga canadensis is native to eastern North America, and T. sieboldii is native to southern Japan (within the native range of HWA, Havill et al, 2016a ) but has been introduced throughout the eastern USA ( Farjon, 2010 ). We hypothesize that microbial α-diversity and community composition will differ among plant-associated habitats and between host species as has been shown previously in hemlock ( Rogers et al, 2018 ) and other tree species such as Populus ( Cregger et al, 2018 ), Ginkgo ( Leff et al, 2015 ) and Broussonetia ( Chen et al, 2020 ). However, we also hypothesize that microbial α-diversity and community composition will also differ across HWA population levels.…”

“…Archaeal/bacterial libraries were prepped for 16S rRNA gene sequencing by means of a two-step polymerase chain reaction (PCR) approach with a mixture of custom 515F and 806R primers (Cregger et al, 2018;Rogers et al, 2018), and for fungi using the ITS2 gene region with a custom mixture of primers (Cregger et al, 2018;Rogers et al, 2018; Supplementary Table S1). An adapter sequence was added to each forward and reverse primer to make them compatible with Nextera XT indexes (Illumina).…”

“…Initial investigations of the hemlock microbiome show that the branch microbiome varies across hemlock species, differing between HWA-susceptible and HWA-resistant species (Rogers et al, 2018). However, among HWA-susceptible hemlock species, the microbiome did not differ significantly between HWA population levels.…”