Water, not carbon, drives drought-constraints on stem terpene defense against simulated bark beetle attack in Pinus edulis
Data files
Oct 20, 2024 version files 65.02 KB
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Drought_transport_df.csv
63.22 KB
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README.md
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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.
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)
See the manuscript for detailed methodological information.