Phytochemistry
To compare the effects of cytotype and genotypic variation on phytochemistry in response to environmental stress, leaves were harvested between August 17-24, 2018. Leaves were collected evenly across the different treatments. From each tree, three fully expanded, young leaves without petioles were collected from the upper third of the tree crown. All leaves collected from defoliated trees showed signs of damage. Leaves from all mesocosms were collected under wet soil conditions. Total condensed tannins were analyzed using the acid butanol method of Porter, Hrstich, and Chan (1985) standardized against purified condensed tannins from P. tremuloides . Levels of the salicinoid phenolic glycosides tremulacin, tremuloidin, salicin and salicortin were quantified using ultra-high-performance liquid chromatography-mass spectrometry as described by Rubert‐Nason, Couture, Gryzmala, Townsend, and Lindroth (2017). Leaf nitrogen was measured using near-infrared reflectance spectroscopy (Rubert-Nason et al., 2013) verified against a subset of the samples analyzed using combustion gas chromatography (Thermo Flash EA1112 elemental analyzer [Thermo Finnigan, Milan, Italy]).