Microbiome Variation Across Two Hemlock Species With Hemlock Woolly Adelgid Infestation.

Nicholas C Dove,Melissa A Cregger,Daniel Simberloff,Veronica A Brown,Christy Leppanen,Anthony V Lebude,James A Fordyce,Timothy J Rogers,Thomas G Ranney

doi:10.3389/fmicb.2020.01528

Abstract

The hemlock woolly adelgid (Adelges tsugae, HWA), an invasive insect, is devastating native hemlock populations in eastern North America, and management outcomes have so far had limited success. While many plant microbiomes influence and even support plant immune responses to insect herbivory, relatively little is known about the hemlock microbiome and its interactions with pathogens or herbivores such as HWA. Using 16S rRNA and ITS gene amplicon sequencing, we characterized the needle, branch, root, and rhizosphere microbiome of two hemlock species, Tsuga canadensis and T. sieboldii, that displayed low and high levels of HWA populations. We found that both archaeal/bacterial and fungal needle communities, as well as the archaeal/bacterial branch and root communities, varied in composition in both hemlock species relative to HWA population levels. While host species and plant-associated habitats explained a greater proportion of the variance in the microbiome than did HWA population level, high HWA populations were associated with enrichment of 100 likely fungal pathogen sequence variants across the four plant-associated habitats (e.g., needle, branch, root, rhizosphere) compared to trees with lower HWA populations. This work contributes to a growing body of literature linking plant pathogens and pests with the changes in the associated plant microbiome and host health. Furthermore, this work demonstrates the need to further investigate plant microbiome effects across multiple plant tissues to understand their influences on host health.

Highlights

A growing body of literature recognizes that microorganisms living inside or in close association with plant tissues are integral to plant health and survival (Compant et al, 2005; Santoyo et al, 2016)
To determine associations between the hemlock microbiome and HWA, we investigated the microbiome of two hemlock species, T. canadensis and T. sieboldii, with different HWA population levels across three plant tissue endospheres and their rhizosphere soils
We detected greater archaeal/bacterial α-diversity in T. canadensis compared to T. sieboldii, but only at q = 0 (q = 0: F1,37 = 8.539, p = 0.006; q = 1: F1,37 = 1.482, p = 0.231)

Summary

Introduction

A growing body of literature recognizes that microorganisms living inside or in close association with plant tissues are integral to plant health and survival (Compant et al, 2005; Santoyo et al, 2016). Expanding our understanding of the reciprocal influences of insect and arthropod herbivores and plant host microbiomes could be useful in instances where plants that are especially important to ecosystem health are under threat. Hemlock loss can have ecosystem-level effects owing to their foundational role in some eastern mixed hardwood forests. They provide habitat for many animals (Yamasaki et al, 2000), moderate diel fluctuations in temperature and moisture that improves stream habitats for many invertebrates (Snyder et al, 2002), and slow biogeochemical cycling, preventing stream eutrophication (Jenkins et al, 1999)

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Conclusion