Abstract:
The goal of this study was to determine whether annual growth ring variables of
young coastal Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco.)
growing in progeny tests are sensitive to availability of soil moisture during the growing season. If ring variables are found to respond to soil moisture deficit (SMD) in
consistent and predictable ways, they might prove useful for screening genotypes for
drought hardiness in breeding programs. Increment cores were collected from 16(18-19 year-old) trees on each of eight progeny test sites in coastal British Columbia. X-ray
densitometry was used to measure eight variables (earlywood and latewood width and
density, latewood proportion, maximum density, latewood mass, and total ring mass) on eleven annual growth rings (years 1985-95) of each core. Regression analyses revealed that all ring variables are strongly influenced by ring distance from the pith (age trends). In addition, after accounting for age-trends, all ring variables were significantly associated with SMD, although the associations were often complex (i.e., involving second and third order polynomials of SMD) and differed significantly across sites. Linear trends in four ring variables (latewood density, proportion, and width; and total ring mass), with increasing SMD, were as expected and were consistent across sites; and thus, show promise in screening for drought hardiness. The remaining ring variables showed inconsistent associations with SMD across sites. A small companion study on cell morphology suggested that latewood cells increase in density with increasing SMD due to decreased cell lumen diameter, and not because of increased cell wall thickness.
