DOI: 10.5061/dryad.tmpg4f57n
title: Water, not carbon, drives drought-constraints on stem terpene defense against simulated bark beetle attack in Pinus edulis

description: 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.
description: See the manuscript for detailed methodological information.
description: # Water, not carbon, drives drought-constraints on stem terpene defense
 against simulated bark beetle attack in Pinus edulis
 **Drought_transport_df.csv** This file describes treatment information as
 well as the local mono- and sesquiterpenes (MST), non-structural
 carbohydrates (NSC), and pressure potential of the inner bark of
 individual trees. Tree: individual identifier Drought: the tree was
 watered (well-watered) or water was withheld (drought) Treatment: unique
 identifier to describe the girdle and inoculation combination (control =
 non-inoculated + non-girdled; I = inoculated + non-girdled; G =
 non-inoculated + girdled; I + G = inoculated + girdled) Girdle: tree was
 girdled or non-girdled Inoculate: tree was inoculated or non-inoculated
 with Ophiostoma fungus Time: time at which sample was collected
 (pre-drought, pre-inoculation, or post-inoculation) Psi: shoot pre-dawn
 water potential (MPa) PressurePotential: inner bark phloem potential
 (MPa); missing data code: na Starch through Fructose: reported as % dry
 weight MT_M1 through MT_terpinolene: individual hydrocarbon monoterpene
 compounds, reported as the amount of compound per gram of dry tissue (mg
 g-1) MTE_4terpineolAcetate through MTE_bornylAcetate: individual
 monoterpene ester compounds, reported as the amount of compound per gram
 of dry tissue (mg g-1) MTO_linalool and MTO_campholenal: individual
 oxygenated monoterpene compounds, reported as the amount of compound per
 gram of dry tissue (mg g-1) ST_35.420 through ST_posLongifolene:
 individual hydrocarbon sesquiterpene compounds, reported as the amount of
 compound per gram of dry tissue (mg g-1) STO_33.366 and STO_cubebol:
 individual oxygenated sesquiterpene compounds, reported as the amount of
 compound per gram of dry tissue (mg g-1)