Contribution of Different-aged Needles to Growth and Wood Formation of Young Red Pines
Abstract:Light-proof coverings were used to isolate Pinus resinosa Ait. needles of different-aged internodes for an entire growing season. The contribution of each complement of needles to growth of the current-year shoot was determined by weekly measurements of internodal extension and needle elongation, and to wood formation by anatomical evaluation of trees harvested periodically. Internodal extension in all treatments was primarily at the expense of reserve foods although additional complements of exposed needles improved growth considerably. The curves of needle elongation of trees with either the 2nd- or 3rd-year needles exposed alone were similar to the uncovered controls, but growth ceased earlier and total growth was reduced. Needles of the current-year shoot, when exposed alone to light, grew continuously with no indication of ceasing at the final harvest date. Diameter of the tracheids comprising the wood of the current-year internode paralleled, in general, the patterns of needle elongation; large-diameter tracheids were produced during periods of active or prolonged needle growth, and the transition to narrow-diameter tracheids was associated with the reduction or cessation of needle growth. The thick tracheid walls, typical of latewood, were first evident when the new shoot attained a certain stage of maturity. Tracheid wall thickness is therefore believed to be a function of net assimilation. Distribution of radial growth, primarily the latewood zone of the growth ring, was strongly influenced by the age of the needles exposed to light. Several probable explanations for the observed growth distributions are presented.
Document Type: Journal Article
Affiliations: Plant Physiologist with the Lake States Forest Expt. Sta., Forest Service, U.S. Dept. Agric., is stationed at the Inst. of Forest Genetics, Rhinelander, Wis.
Publication date: 1964-06-01
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