May 16, 2024
Journal Article

Hotter droughts increase resource allocation to chemical defenses in piñon pine

Abstract

? Heat and drought affect plant chemical defenses and thereby plant susceptibility to pests and pathogens, but how they do so in mature trees remains largely unknown. Monoterpenes play critical roles in tree chemical defense against bark beetles. We measured needle and woody tissue monoterpene concentrations and primary physiology from mature piñon pines (Pinus edulis) in a large-scale temperature and drought manipulation field experiment. ? Heat had no effect on total monoterpene concentrations, but trees under combined heat and drought stress exhibited ~85% and 35% increases in needle and woody tissue, respectively. These elevated levels were sustained in new growth over multiple years. ? Physiological variables, including growth, each explained less than 10% of the variation in total monoterpenes for both tissue types while starch and glucose + fructose measured one-month prior explained ~25% of woody tissue total monoterpenes, suggesting a critical role for non-structural carbohydrates in supporting monoterpene production under stress. Shifts in key monoterpene compounds with known roles in bark beetle ecology were observed with important implications for tree susceptibility to biotic attack. ? Our results point to sophisticated shifts in monoterpene production where cumulative climate effects reprioritize carbon sources and sinks and thus allocation toward defense.

Published: May 16, 2024

Citation

Trowbridge A., H.D. Adams, A.D. Collins, L.T. Dickman, C. Grossiord, M. Hofland, and S. Malone, et al. 2021. Hotter droughts increase resource allocation to chemical defenses in piñon pine. New Phytologist 197, no. 4:921–938. PNNL-SA-156752. doi:10.1007/s00442-021-05058-8