The role and pattern of phenotypic plasticity in ecological specialization of plants

Abstract

Phenotypic plasticity and ecological specialization play vital roles in plant adaptations across habitats. These two fundamental strategies appear to be opposing due to the assumption that specialization reduces the ability (i.e. plasticity) to respond environmental changes. Despite extensive research on phenotypic plasticity, our understanding of this complex property is still limited. This thesis examines the interplay between plasticity and specialization together with reproductive and competitive strategies of plants. Firstly, I conducted a data-synthesis for the first time in literature to test specialization hypothesis and the role of reproductive strategies in habitat specialization. I found that non-clonal plants expressed greater plasticity than clonal plants. Moreover, specialization to relatively benign habitats did not result in greater performance plasticity; contrary to the specialization hypothesis predictions. Secondly, I examined plasticity and consequences of specialization in an altitudinal gradient following a population expansion from relatively good to more stressful habitats. I tested if specialization is linked with a general loss of plasticity. Specialization to a higher abiotic stress was associated with adaptive plasticity loss in functional traits. Therefore, specialization may limit plant responses to future environmental changes. Thirdly, I studied how simulated competition affects plant life histories and growth forms, and the role of shade avoidance plasticity. I found that all of our species invested more to reproduction under simulated competition. Interestingly, I also found that shade avoidance plasticity can increase reproductive efficiency. Therefore, shade avoidance can be regarded as a strategy to increase reproduction and not only a competitive strategy as has been predicted. Lastly, I tested specialization hypothesis along an environmental stress gradient by comparing plastic responses of a high stress mine site and low stress adjacent area populations. There was no performance difference between populations across pH treatments. The overall result did not support the specialization hypothesis and suggested that the species have invaded mine sites are either extreme generalists or retain stress tolerant genotypes. In conclusion, although the evolution of specialization is common in nature, plasticity expression in my experiments did not follow the patterns predicted by the specialization hypothesis.