Metabolite tissue collection and processing
Leaf samples were harvested in mid-June one week prior to the first
heatwave event of 2016 and 2017. Late-August samples were harvested
three days after the final heatwave of 2016 and 2017 for metabolite
analysis. Fresh tissue of 2-4 healthy mature birch leaves or one spruce
branchlet from the current year’s growth was removed from each plant (n
= 4-6 plants per treatment) using a razor blade. The foliage was
immediately put into liquid nitrogen and then transferred to a
-20○C freezer to await processing. The samples were
freeze-dried, ground using a mini Wiley Mill (Thomas Scientific,
Swedesboro, NJ) and then passed through a 0.85 mm sieve (#20 mesh). The
dried samples were stored at -20○C until analysis.