XVI International Botanical Congess

Survival and fitness of plants is largely determined by their ability to respond to changes in environmental conditions, especially to variability in the supply of essential resources such as light, water and nutrients. Plastic responses are the result of an evolutionary history, with environmentally-caused selection pressures and developmental constraints as the main opposed forces. Costs and benefits of phenotypic plasticity, as well as constraints acting on the evolution of environmentally-induced changes in development, are likely to differ between environments and traits. This lecture will explore how plastic responses of stem internodes and petioles to light limitation can vary according to their spatial orientation, and it will seek to identify ecological causes and consequences of strikingly different patterns of plasticity in closely related species. The results of experimental studies suggest that different costs and benefits are associated with the expression of spacer plasticity in horizontal and vertical space. These response patterns will be discussed in terms of underlying selection pressures, and their ecological consequences for plant performance in a heterogeneous natural environment will be addressed.