Ecophysiological consequences of differences in plant size: abscisic acid relationships in the epiphytic orchid Dimerandra emarginata

Abstract

Changes in abscisic acid (ABA) content and several water relations parameters were studied in the epiphytic orchid Dimerandra emarginata in the tropical lowlands of Barro Colorado Island, Panama. Similar to previous observations of size dependency of physiological parameters in vascular epiphytes, we found significant differences in ABA accumulation (both in terms of temporal patterns and amount) in small and large plants under drought stress. The highest values of ABA content in leaves, stems, and roots were found in the smaller specimens, reaching the levels of poikilohydric resurrection plants. Substantial accumulation of ABA occurred after stomatal closure, indicating other functions of ABA than stomatal regulation in this bark epiphyte.

Physiological and growth responses of Populus davidiana ecotypes to different soil water contents

“…Effect of watering was highly significant (Po0.001), and interaction effects between watering and ecotype were also significant in these properties except for d 13 C. It showed that the dry climate ecotype exhibited a distinctly higher WUE T , WUE i , ABA and d 13 C than the wet climate ecotype under low soil water contents. Interestingly, ecotypic differences in ABA and d 13 C were less in high soil water contents than in low soil water contents, suggesting that relationships between physiological responses and drought adaptations were complicated by internal drought tolerance mechanisms and external environmental factors such as water availability, or their interaction (Brodribb and Hill, 1998;Amdt et al, 2001;Zotz et al, 2001;Ponton et al, 2002;Sharp, 2002). In addition, although d 13 C was increased significantly by low soil water contents, no interaction between ecotype and watering was detected, which is consistent with most previous studies (e.g.…”

“…Some of the adaptive responses to water deficit are physiological and morphological changes, such as changes in plant structure, growth rate, tissue osmotic potential and stomatal conductance (Jones, 1992;Larcher, 1995). On the other hand, abscisic acid (ABA), a well-known stress-inducible plant hormone and growth inhibitor, has long been studied as a potential mediator for induction of drought tolerance in plants (Zhang and Davies, 1989;Chen et al, 1997;Zotz et al, 2001;Sharp, 2002). ABA seems to play a predominant role in the conversion of environmental signals into changes in plant gene expression (Bray, 2002;Zhu, 2002).…”

Ecophysiology and Plant Size in a Tropical Epiphytic Fern, Asplenium nidus, in Taiwan

“…For example, photosynthetic rates of leaves are not expected to vary dramatically, provided such rates are compared on an equal area or mass basis. Recent studies by Zotz and colleagues, however, indicate that ignoring plant size in physiological studies may lead to erroneous conclusions (Zotz 1997;Zotz et al 2001aZotz et al , 2001b. They provide convincing evidence that, at least in some epiphytic taxa, physiological parameters of leaves can vary depending on the size of the plant selected for measurement.…”

“…Differences in leaf morphology may explain some effects of plant size , although and Zotz et al (2001aZotz et al ( , 2001b argue that size-related differences in biomass allocation as they relate to plant water relations correlate well with differences in the functioning of plants of different sizes. Clearly, more work is needed to understand the mechanisms underlying differences in physiology that correlate with plant size.…”

“…They provide convincing evidence that, at least in some epiphytic taxa, physiological parameters of leaves can vary depending on the size of the plant selected for measurement. The bulk of their evidence is derived from ecophysiological investigations of an epiphytic bromeliad, Vriesea sanguinolenta , although and Zotz et al (2001aZotz et al ( , 2001b provide some evidence that plant size affects the physiology of several epiphytic ferns, aroids, and orchids. In addition, results of other studies indicate that plant size, although not always clearly differentiated from plant age, can be an important variable influencing the physiology of terrestrial taxa, particularly trees (Kull and Koppel 1987;Miller et al 1990;Ryan and Waring 1992;Grulke and Miller 1994;Schoettle 1994;Yoder et al 1994;Smith and Resh 1999;Kolb and Stone 2000;Grulke and Retzlaff 2001).…”