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

Ecotype specialization and phenotypic plasticity in response to resource availability and variable developmental time.

Zaitchik, Benjamin¹, Novoplansky, Ariel¹, ¹

ABSTRACT- Initiation of and allocation to an organ depend on the availability of limited resources and on the probability the organ will mature. We hypothesized that adaptations to low and unpredictable resource levels and developmental time include the development of small modules and early initiation of flowering, as these adaptations reduce the risk of losing invested resources. The semi-desert environment, characterized by highly variable rainfall, encourages such a deterministic approach. The Mediterranean ecosystem, with greater auto-correlation of rainfall, favors plasticity in response to soil water status. In a greenhouse experiment we found that excess water encouraged accelerated growth and early flowering in semi-desert populations of the annual Trifolium purpureum, while Mediterranean plants responded with temporally distributed growth that ultimately yielded more, larger branches supporting more inflorescence. Mediterranean plants were also expected to exhibit greater plasticity in response to germination date, since inter-annual variability is lower in the Mediterranean ecosystem. This prediction was confirmed, as only Mediterranean plants responded to a delayed germination treatment with significant changes in branch architecture. We conclude that Mediterranean plants take a more "optimistic" approach to development, scheduling development around environmental signals trusted to be reliable. Semi-desert plants are relatively "pessimistic," tending to exploit available resources in a rapid, deterministic manner regardless of environmental conditions.

KEY WORDS: developmental plasticity, ecotypic differences, resource allocation, architecture