The rhizosphere microbial community of adelgid infested eastern hemlock trees

Background/Question/Methods

Decline of the Eastern Hemlock, Tsuga canadensis, is known to be associated with infestation of the hemlock woolly adelgid, Adelges tsugae. However, not all trees are affected equally. For the purpose of this study, the effect of hemlock infestation on the host’s rhizosphere fungal community was observed. Soil samples were collected from infected and non-infected hemlocks from the Stokes State Forest of Northwestern New Jersey.  Through use of molecular techniques, DNA fingerprinting using fungal specific primers was performed. DNA was extracted from the rhizosphere of infested and non-infested hemlocks, amplified by PCR using fluorescently labeled primers, and digested with restriction enzyme HhaI.  We then performed terminal restriction length polymorphism (tRFLP) followed by statistical analysis to determine if tree health and adelgid infestation interact with rhizosphere fungal communities.  The tRFLP fingerprints were compared to the tree’s diameter at breast height, root starch content, and estimates of infestation intensity on the tree limbs (total foliar length versus current foliar length).  

Results/Conclusions

No significant correlation between the infestation level, tree health, and fungal community composition was found.  Further, starch content of the roots was not affected by herbivory.  This result suggests that the roots and rhizosphere fungal communities may be robust to above ground herbivory in this system.  Future work will include analysis of the effect of adelgid herbivory on rhizosphere bacterial communities.