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).