Abstract
A knowledge of how genotypes, populations and species respond to environmental variation is important for understanding the likely impacts of future climate change. Plasticity is the environment-specific response of a genotype to environmental variation within a generation and can be adaptive or maladaptive. Plants are ideal organisms to study plasticity, for example using field transplants, however root systems are difficult to study in the field. Therefore, intensive laboratory experiments on root systems compliment large field studies of plasticity.This study used a species of ragwort, Senecio chrysanthemifolius, to assess the plasticity and specific root trait responses of genotypes to drought and temperature stress. Field experiments identified two types of responses to changing environments, showing higher and lower relative fitness or flower number, outside the species’ home range. Twenty-four genotypes (12 of each type) were identified and used in the current study. To test the plasticity of root systems, I used a fully-crossed experimental design of low and high drought and temperature treatments. I used multiple cuttings of each genotype, grown in vertical agar plates, allowing assessments of root architecture for the same genotype in multiple environments.
The 12 genotypes identified as showing increased relative fitness outside the range in the field, possessed smaller shoots and larger root:shoot ratio, relative to the other genotypes. This suggests that genotypes with larger root:shoot ratios may show an increase in relative fitness outside their home range. Increased temperature resulted in increased root diameters, and deep, narrow root systems, whereas high drought stress resulted in overall smaller root systems. Plasticity was observed in root traits across treatments, and genotype-by-environment response among all 24 genotypes was not detected. However, a lack of GxE interactions in the plastic response of root traits suggests strong stabilising selection for the observed response, and therefore observed differences in fitness in the field are unlikely to be due to plasticity in root traits.
| Date of Award | 12 May 2020 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Claire S Grierson (Supervisor) & Jon Bridle (Supervisor) |