Astringency of douglas-fir foliage in relation to phenology and xylem pressure potential

Astringency (tannin content) of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] foliage was examined in relation to phenology and water status. Foliage was sampled from control trees, trees on south-facing slopes, and trenched trees prior to budbreak and at periods of two, six, and 12 weeks after budbreak. Astringency of prebudbreak foliage from untrenched trees was comparable to that of mature foliage. Foliage expansion was accompanied by dilution of the tannin content. Percent relative astringency of control trees was significantly and positively related to the absolute value of predawn xylem pressure potential, while this relationship was negative for trees in the south-facing group. Coefficients of determination for the relationship between astringency and predawn xylem pressure potential were high (0.67 and 0.79 for the control and south-facing groups, respectively). Astringency of foliage from trees in the south-facing group also was affected significantly by daytime xylem pressure potential. Astringency of foliage from trees in the control and south-facing groups was not significantly related to tissue age, while that from trenched trees was significantly related only to age. Results demonstrate that water status is a better predictor of foliage astringency than is tissue age in unperturbed trees of this species and that, depending on the magnitude and/or timing of water deficits, opposite relationships between astringency and xylem pressure potential can be observed.