Apple, M., K. Tiekotter, M. Snow, J. Young, A. Soeldner, D. Phillips, D. Tingey, B.J. Bond. 2002. Needle anatomy changes with increasing tree age in Douglas fir. Tree Physiology 22:129-136.
Morphological differences between old growth and sapling (Pseudotsuga menziesii, (Mirb.) Franco) Douglas fir trees may extend to differences in needle anatomy. We used microscopy with image analysis to compare and quantify anatomical parameters in cross-sections of previous year needles of old growth and sapling Douglas fir trees at the Wind River Canopy Crane in Washington and at three sites in the Cascade Mountains of Oregon. We also compared needle anatomy across a chronosequence of 10, 20, 40, and 450-year-old Douglas fir trees from the Wind River site. Anatomy differed significantly between needles of old growth and sapling Douglas fir trees at all sites. This suggests a developmental change in needle anatomy with increasing tree age and suggests that the influence of tree age on needle anatomy is greater than that of site, canopy level, or year. Needles of saplings had proportionately smaller vascular cylinders, larger resin canals, and few hypodermal cells. In contrast, needles of old-growth trees were shorter, had proportionately larger vascular cylinders, smaller resin canals, and numerous hypodermal cells. Astrosclereids, which sequester lignin in their secondary cell walls and occupy space otherwise filled by photosynthetic cells, were scarce in needles of saplings but abundant in needles of old-growth trees. Needles of old-growth trees had an average of 11% less photosynthetic mesophyll area than needles of saplings. The percentage of non-photosynthetic area increased significantly with increasing tree age in needles from the chronosequence of 10, 20, 40, and 450-year-old trees at the Wind River site. This reduction in photosynthetic area may contribute to decreased growth rates in old trees.