Phenotypic Plasticity: An Important Source Of Phenotypic Variation In Plants

Phenotypic plasticity is an important attribute of plants which enables them to survive across a range of environments. Although plasticity is widely studied, majority of the studies were conducted in relatively simple environments. Also most studies have defined plasticity in terms of the relative allocation of biomass between two compartments. This ignores the potential contribution of other traits that could tell something about a plant's strategy. The modular organization of plants suggest that, the plasticity of the whole plant depends on the plastic responses of both number and individual characters of traits, with the consequence that plant traits could differ in magnitude of plastic responses to different resources, and thus resulting in a"hierarchy"of plastic responses amongst traits. Only a few studies have considered the magnitude of plasticity amongst traits.In this study, we tested the hypothesis that differences in germination timing and population density for plants growing in the field will lead to significant plasticity not only in biomass traits, but architectural traits that enhances the capture of limited resources. We also used the knowledge of phenotypic plasticity to enhance the understanding of crop response to farm management practices.In Fagopyrum esculentum grown under different density and sowing date, there was significant plasticity in stem mass ratio, leaf mass ratio and leaf to root ratio, as well as single measures of stem length, stem diameter, branch length and number of branches. Computation of coefficient of variation (CV) indicated some consistency in magnitude of trait plasticity for both density and sowing date treatments. In a colonizing population of Datura stramonium, there was significant plasticity in specific leaf area, leaf area ratio and number of leaves; traits that are associated with light capture in response to high density. Similarly, this species exhibited significant plasticity in reproductive allocation in response to the limitation of four environmental factors. When their plasticity patterns were compared, buckwheat displayed plasticity in competitive structures, millet on the other hand, preferred to display more plasticity in reproductive allocation. These different responses could influence the way these two crops would response to high density. For buckwheat, the loss in yield at high density could be attributable to the plastic increase in competitive structures instead of allocation to reproduction. Conversely, for Millet sown at high density, yield loss was prevented due to the increased in reproductive allocation. This thesis demonstrate that plasticity is a major source of phenotypic variation in the real world, contrary to the earlier (neo- Darwinian) view of this as trivial'noise.