PARENT SESSION
Poster Session #32: Plant Ecology I.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Ecotypic differences in response to resource availability and photoperiod signals.

Acuņa, Tania ¹, Novoplansky, Ariel¹, ¹

ABSTRACT- This study focuses on the ways plants from contrasting ecological backgrounds change their size and architecture in response to the availability of limiting resources and photoperiodic signals. We hypothesized that adaptations to low and unpredictable resource levels and developmental time include the development of a larger number of relatively small organs, reducing the risk of losing invested resources. Trifolium purpureum Loisel. plants were collected from Mediterranean (high and more predictable resources) and semi-desert (low and and less predictable resources) populations in Israel. The plants were grown under HIGH and LOW water and three photoperiod treatments: (a)"eternal spring"-short nights throughout the growth season, (b)"early spring"-short nights starting seventy days before the end of the growth season, and (c)"control"-natural photoperiod conditions. Under natural photoperiod conditions, the Mediterranean plants developed "optimistically", producing larger organs throughout the season. In contrast, semi-desert plants developed more "cautiously", with smaller organs. Under "eternal spring" conditions, plants from both sources flowered and senesced earlier compared to the controls. Under "early spring" conditions, the semi-desert plants terminated their vegetative development very soon after the onset of the photoperiod treatment while the Mediterranean plants continued their vegetative development similarly to the controls. It is suggested that the significance of environmental signals can be as high as resource availability and that their interpretation is highly evolutionary-dependent.

KEY WORDS: ecotype specialization, photoperiod, phenotypic plasticity, environmental predictability