© 2000 Heron Publishing—Victoria, Canada
Thigmomorphogenesis: changes in the morphology and mechanical properties of two Populus hybrids in response to mechanical perturbation
Michele L. Pruyn (1), Benjamin J. Ewers, III (2) and Frank W. Telewski (3)
1. Department of Forest Products and Department of Forest Science, Forest Research Laboratory, Richardson Hall, Oregon State
University, Corvallis, OR 97331-7402, USA (pruynm@frl.orst.edu) / 2. Orthopaedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, East Lansing, MI 48824,
USA / 3. Department of Botany and Plant Pathology, W.J. Beal Botanical Garden, Michigan State University, East Lansing, MI 48824, USA / Received January 30, 1998
Summary
To identify hybrid-specific differences in developmental response to mechanical perturbation (MP), we compared the effects
of stem flexure on several morphological and mechanical properties of two Populus trichocarpa Torr. & A. Gray × P. deltoides Bartr. ex Marsh. hybrids, 47-174 and 11-11. In response to the MP treatment, both hybrids exhibited a significant increase in radial
growth, especially in the direction of the MP (47-174, P = 0.0001; 11-11, P = 0.002), and a significant decrease in height to diameter growth ratio (P = 0.0001 for both hybrids), suggesting that MP-treated stems are more tapered than control stems. A direct consequence of
the MP-induced increase in radial growth was a significant increase in flexural rigidity (EI, N mm2) in stems of both hybrids (47-174, P = 0.0001; 11-11, P = 0.009).
Both control and MP-treated stems of Hybrid 47-174 had significantly greater height to diameter ratios and EI values than
the corresponding stems of Hybrid 11-11 (11-11 stem ratios and EI values were 85 and 76%, respectively, of those of 47-174).
In Hybrid 47-174, Young's modulus of elasticity (E, N mm–2), a measure of stem flexibility, for MP-treated stems was only 80% of the control value (P = 0.0034), whereas MP had no significant effect on E of stems of Hybrid 11-11 (P = 0.2720). Differences in flexure response between the hybrids suggest that Hybrid 47-174 can produce a stem that is more
tolerant of wind-induced flexure by altering both stem allometry and material properties, whereas Hybrid 11-11 relies solely
on changes in stem allometry for enhanced stability under MP conditions.
Keywords:
developmental acclimation, flexural rigidity, plantation forestry, second moment of cross-sectional area, wind tolerance,
Young's modulus of elasticity.
