Intraspecific variation in Tsuga canadensis foliar chemistry

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Three groups of Tsuga canadensis (Eastern Hemlock) trees were analyzed to compare their chemical composition and the potential for naturally occurring resistance to Adelges tsugae (Hemlock Woolly Adelgid [HWA]). Potentially resistant "parent" trees located in southern Connecticut were compared with rooted propagules from those same trees and control trees located in northern Vermont, outside of the current HWA range. For trees in each group, we quantified Ca, P, K, C, and N and developed terpenoid profiles using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC/MS). There was no significant variation in terpenoid profiles between the three groups of hemlock trees. Propagules retained elevated levels of Ca and N from fertilization during propagation, suggesting that their chemical composition does not mirror the parent trees. The potentially resistant "parent" trees had higher levels of K compared to control trees. This may impart some level of tolerance/resistance to HWA and explain their persistence in hemlock forests that have otherwise been decimated by HWA. Comparison to regional foliar chemistry databases suggest that while rare, such elevated K levels do exist in natural hemlock populations. Such individuals may persist as HWA continues to spread across the region.

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Northeastern Naturalist