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School of Life Sciences' Friday Seminar

Dissertation Defense: "Trait Variation as Plants Grow Up: Simultaneous Effects of Ontogeny and Phenotypic Plasticity" - Speaker: Ana Flores, Botany PhD candidate * Abstract: Plant ontogeny is the genetically regulated transition through developmental stages. Master regular genes control the switch from juvenile to adult phase change and later to reproductive stage. The juvenile-adult transition is the most well-studied ontogenetic variation, and so we have considerable evidence that these shifts in form and function occur for all plant types. In some plants, the transition is coupled with conspicuous morphological change, called heteroblasty. For other plants, the ontogenetic transition is subtle, and therefore difficult to discern. Ontogenetic patterns are believed to have evolved in response to predictable environmental change across a plant’s life. However, environmental change is not always predictable, and plants have also evolved phenotypic plasticity as a key strategy in unpredictable environments. Together, ontogeny and phenotypic plasticity create complex, nonlinear trajectories of trait expression, and the relative contribution of each to plant phenotypes is unknown. Additionally, ontogenetic patterns of functional traits across early establishment stages (seedlings, e.g.) are relatively unexplored. These early stages are essential for plant regeneration and population stability, yet we know less about ontogenetic shifts in their trait expression, and potential plasticity in trait patterns. The main objective of this work is to address these two research gaps. With the first chapter, I begin to uncover the mechanism by which plants exhibit plasticity in whole-plant trajectories in response to abiotic factors, and whether these trajectories follow predicted ontogenetic shifts in functional traits, in a greenhouse experiment on the native Hawaiian prickly poppy, pua kala (Argemone glauca). Eco-physiological and defense traits shifted considerably across stages, and ontogenetic trajectories demonstrated phenotypic plasticity in response to both light and water availability. Leaf area and quantum efficiency were plastic, differing between light and water treatments, especially in the seedling to juvenile transition. Prickle density and latex alkaloid concentration increased across ontogeny, but the magnitude of these trajectories was significantly influenced by water availability. This study shows that as plants develop through ontogeny, they become more acquisitive and better defended, and the magnitude of these trajectories varies particularly with respect to water. With the second chapter, I characterize ontogenetic patterns in early, post-germination stages, and test whether these patterns exhibit plasticity in a simulated drought experiment on Acacia koa, an endemic Hawaiian tree with ecological and cultural significance. Plasticity was quantified for photosynthetic and leaf morphological traits within three early stages: cotyledon, seedling, and young juveniles. Multivariate analyses revealed that koa seedling traits were weakly correlated along two functional axes, but these were not influenced by drought. Univariate analyses revealed significant plasticity of individual physiological traits in cotyledon-seedling stage, and in physiological and morphological traits in seedling-juvenile stage. However, highly reduced growth under drought conditions reveals low tolerance despite trait plasticity, indicating potential decline in Hawaii’s second most abundant native tree. In the third chapter, I used meta-analysis to synthesize functional trait patterns in early phase change (germinant to seedling, and seedling to juvenile), and tested for possible effects of growth form, trait type, habitat, and biome across 54 plant species. There were strong shifts in anatomical traits, specifically stomatal pore index, which increased from early to late phase. Leaf area and leaf thickness increased, as well, while specific leaf area decreased. No effect of phase, habitat, form, or biome was detected. Considerable work has been done to show that ontogenetic trajectories of functional traits are nonlinear, complex phenotypes that describe plant resource use across development. We know that they differ in direction and magnitude, and here I show that they are also not all fixed. In early ontogeny, these patterns can be plastic in response to low water, however, it may not be sufficient to overcome the negative effects on growth. Finally, I identified significant gaps in our knowledge about early ontogenetic variation. As climate change scenarios indicate that drying events are increasingly unpredictable, early acclimation via phenotypic plasticity will be critical to seedling survival beyond vulnerable establishment stages. Future research on these understudied ontogenetic stages, like cotyledon-stage plants and seedlings with first true leaves, along with a wider breadth of trait types, will provide more insights into early plant function.

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