Circum-Arctic distribution of chemical anti-herbivore compounds arctic shrubs

Spatial variation in plant chemical defence towards herbivores can help us understand variation in herbivore top-down control of shrubs in the Arctic and possibly also shrub responses to global warming. Less defended, non-resinous shrubs could be more influenced by herbivores than more defended, resinous shrubs. However, sparse field measurements limit our current understanding of how much of the circum-Arctic variation in defence compounds is explained by taxa or defence functional groups (resinous/non-resinous). We measured circum-Arctic chemical defence and leaf digestibility in resinous (Betula glandulosa, B. nana ssp. exilis) and non-resinous (B. nana ssp. nana, B. pumila) shrub birches to see how it varies among and within taxa and functional groups. Using LC-MS metabolomic analyses and in-vitro leaf digestibility via incubation in cattle rumen fluid, we analysed defence composition and leaf digestibility in 128 samples from 44 tundra locations. We found biogeographical patterns in anti-herbivore defence where mean leaf triterpene concentrations and twig resin gland density were greater in resinous taxa and mean concentrations of condensing tannins were greater in non-resinous taxa. This indicates a biome-wide trade-off between triterpene or tannin dominated defences. However, we also found variations in chemical defence composition and resin gland density both within and among functional groups (resinous/non-resinous) and taxa, suggesting these categorisations only partly predict chemical herbivore defence. Complex tannins were the only defence compounds negatively related to In-Vitro Digestibility, identifying this previously neglected tannin group as having a potential key role in birch anti-herbivore defence. We conclude that circum-Arctic variation in birch anti-herbivore defence can be partly derived from biogeographical distributions of birch taxa, although our detailed mapping of plant defence provides more information on this variation and can be used for better predictions of herbivore effects on arctic vegetation.

Chemical defense compound concentrations was quantified using LC-MS metabolomic analyses. In-vitro digestibility was measured as in-vitro organic matter digestibility (IVOMD) by incubating dry leaf material in cattel rumen fluid at 38°C for 96 hours an then calculating the proportion of digested organic material. Leaf nitrogen and carbin content was measured using an elemental analyser interfaced to a continous flow isotope ratio mass spectrometer. Leaf chemisty and digestibility were all measured using dired and ground leaf material. Resin gland density was calculated as number of resin glands per mm2 on 15 mm twig segment starting 20 mm from the twig top on current annual growth (CAG) twigs. Specific Leaf Area was measured as a proxy (SLA-P) by calculating dry leaf area/dry mass. Environmental data was retrieved as interpolated grid data with a resolution of 30 arc seconds (~1 km) from the Worlclim database and then extracted using GIS software ArcMAP.

The data file includes metadata and a sheet with data explanation, including units for all measures.

Lindén, Elin; te Beest, Mariska; Abreu, Ilka et al. (2022). Circum-Arctic distribution of chemical anti-herbivore compounds arctic shrubs [Dataset]. Dryad. https://doi.org/10.5061/dryad.9p8cz8whd