Non-structural carbohydrate and diterpene resin analyses of xylem
We collected increment cores (5 mm dia.) from all trees throughout the experiment. Two cores were taken from opposite sides of each tree once a month from July to November, 2014 and from May to September, 2015 (n=20 cores per tree). We used these cores to determine concentrations of NSCs and diterpene resin acids in the xylem over time. At each sampling date we selected the most current two consecutive rings from each of the two cores as the single year core did not provide enough tissue to conduct both NSC and diterpene analyses. For instance, in July 2014, we pooled the complete growth ring from 2013 and the partial (until July) ring from 2014. We freeze-dried these cores for six days (Labconco Corp., Kansas City, MO, USA) and ground them with a grinder (Tissue Lyzer II, QIAGEN, GER) for 20-30 seconds at a frequency of 30 sec-1. Ground samples were then separated into two groups: One group was for NSC analysis (12-14 mg) and the other was for diterpene analysis (25-27 mg).