© 1993 Heron Publishing—Victoria, Canada
Maturation in larch: age-related changes in xylem development in the long-shoot foliage and the main stem
Yasuo Takemoto and Michael S. Greenwood
Department of Forest Biology, University of Maine, Orono, ME 04469, USA / Received February 10, 1993
Summary
As the meristems of eastern larch (Larix laricina (Du Roi) K. Koch) mature, they produce long-shoot foliage with progressively higher chlorophyll content and net photosynthesis
and progressively lower specific leaf area (Hutchison et al. 1990). Despite the apparent increase in foliar vigor, both shoot
height and diameter growth rates declined during maturation. These changes were associated with changes in xylem morphology
of the vascular tissue of both the long-shoot foliage and the main stem. Although the number of xylem cells remained constant
in a cross section of the foliage, their diameters increased with age. With increasing maturation, the same number of xylem
cells were produced per radial file in the
annual rings of the main stem, but their radial diameters decreased, which accounted for the decrease in diameter growth.
There was no change in tracheid length during maturation. We conclude that the decrease in growth rate with increased maturation
is not due to a decrease in physiological vigor of the foliage, but is a function of reduced sink strength of the growing
shoots.
Keywords:
diameter growth rate, foliar chlorophyll content, height growth rate, Larix laricina, net assimilation rate, phase change, sink strength, specific leaf area, tracheid length, xylem cell diameter.
