PARENT SESSION
Oral Session 10: Physiology I: Temperature, Light, and Growth.
Presiding: C Knight
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room C 123.
Effects of mechanical stress and canopy shading on plant growth patterns and consequences for life-time performance.
Anten, Niels*,1, Casado-Garcia, Raquel2, Nagashima, Hisae3, 1 Department of Plant Ecology, Utrecht, The Netherlands2 Area de Ecologia, Universidad de Cordoba, Cordoba, Spain3 Nikko Botanical Garden, University of Tokyo, Nikko, Japan
ABSTRACT- The plastic increase in stem elongation in dense vegetation is generally believed to be induced by canopy shading, but because plants protect each other against wind, wind shielding (reduced mechanical stress) could also play a role. We examined the interactive effects of canopy shading and mechanical hardening on plant growth. Tobacco (Nicotiana tabacum) plants were flexed 0 (control plants) or 40 (flexed plants) each day and grown either in isolation, in a dense mono stand (with only flexed or only control plants) or in a mixed stand (flexed and control plants grown together). Compared to control plants, flexed plants produced shorter and thicker stems, which were more flexible (lower elastic modulus) but had equal maximum break stress. Consequently, they were estimated to resist 40 to 70% greater wind forces and had 60 to 500% greater buckling safety factors. Plants from the stands produced taller thinner stems than isolated plants. The growth response to mechanical stress was independent of canopy shading. For isolated plants and the plants in the mono stands the increase in stability in flexed plants had no consequences for either growth or seed production. By contrast, in the mixed stand flexed plants were progressively shaded by control plants and had considerably lower rates of seed production and survival. These results indicate that the plastic increase in stem elongation of plants in dense vegetation is not only induced by canopy shading but also by wind shielding. The additional stem elongation induced by wind shielding has import consequences for the competitive ability and life-time seed production.
Key words: competition, fitness, biomechanics, growth