Skip to main content
Dryad

Water, not carbon, drives drought-constraints on stem terpene defense against simulated bark beetle attack in Pinus edulis

Malone, Shealyn1; Thompson, R. Alex2; Chow, Pak S.3; de Oliveira Jr., Celso R.4; Landhäusser, Simon M.3; Six, Diana L.5; McCulloh, Katherine A.4; Adams, Henry D.6; Trowbridge, Amy M.4

Research facility: University of Wisconsin System
Published Oct 20, 2024 on Dryad. https://doi.org/10.5061/dryad.tmpg4f57n

Data files

Oct 20, 2024 version files 65.02 KB

Abstract

Drought predisposes forest trees to bark beetle-induced mortality, but the physiological mechanisms remain unclear. While drought-induced water and carbon limitations have been implicated in defensive failure and tree susceptibility, evidence demonstrating how these factors interact is scarce. We withheld water from mature, potted Pinus edulis (Engelm.) and subsequently applied a double-stem girdle to inhibit carbohydrate transport from the crown and roots. Within this isolated segment we then elicited a defense response by inoculating trees with a bark beetle-fungal symbiont (Ophiostoma sp.). We quantified local mono- and sesquiterpenes (MST), non-structural carbohydrates (NSC), and pressure potential of the inner bark. Both drought-stressed and watered trees had similar NSC concentrations just prior to inoculation and depleted NSC similarly following inoculation, yet MST induction (i.e., increased concentration and altered composition) was constrained only in drought-stressed trees. Thus, NSC consumption was largely unrelated to de novo MST synthesis. Instead, stoichiometric calculations show that induction originated largely from stored resin. Watered trees experiencing higher pressure potentials consistently induced higher MST concentrations. We demonstrate the importance of preformed resin towards an induced MST response in a semi-arid conifer where drought-constraints on defense occurred through biophysical limitations (i.e., reduced turgor hindering resin transport) rather than through substrate limitation.