Decoupling of height growth and drought or pest resistance tradeoffs is revealed through multiple common-garden experiments of lodgepole pine

We selected five lodgepole pine populations, representing a total of 224 maternal half-sib families, grown in four progeny test sites (> 35 yrs) located along various climatic gradients in central Alberta, Canada. Across the four progeny test sites, we chose a total of 1,490 trees for phenotyping. Height growth (m) was measured at age 35-yr with a clinometer. Carbon isotope ratio (δ13C, in ‰) analysis was performed at Alberta Innovates in Victoria, using outside slabs cut and ground from the 5 mm increment cores taken from the north side of each tree at approximately breast height (1.3 m) at age 35. Samples were analyzed using an established method on a MAT253 Mass Spectrometer with Conflo IV interface and a Fisons NA1500 EA. We assessed the severity of WGR infection in the test sites by a qualitative scoring system with discrete categories ranging from no gall symptoms to deceased (four tiers) for all trees sampled at age 36-yr. We also investigated these trees’ suitability to MPB. Host tree suitability to the beetles was evaluated by quantifying defense chemicals (mainly monoterpenes) using a Gas Chromatography/Flame Ionization Detector based on cambial tissues collected by a hole punch when trees were actively growing, coinciding with MPB flight in western Canada. Then, chemical profiling was performed to test against MPB performance based on laboratory bioassays. A cutoff of four categories was used to classify trees with different MPB suitability levels. In addition, we performed dendrochronological analysis to calculate drought resistance indices based on changes in tree-ring width before and after drought event.