Competition in Arabidopsis thaliana (L.) Heynh., behaviour of Mimosa pudica L. and a new method to characterize roots demonstrated with Helianthus annuus L..

  • Author / Creator
    Nguyen-Phuc, Bao Tan
  • In this dissertation, I address 5 problems in the discipline of plant ecology: two problems in plant competition, two problems in plant behaviour and one problem in the phenotyping of plant roots. First, we directly test Darwin’s competition-relatedness hypothesis with a pairwise competition experiment using 14 accessions of Arabidopsis thaliana (L.) Heynh. We do not find support for Darwin’s contention that more closely related individuals compete more fiercely, or its underlying assumptions. In fact, under higher resource conditions, we show that kin compete less fiercely than strangers, and interestingly this pattern goes away with lower resource conditions. Within the context of our modern understanding of the genetics of traits, these results challenge a key assumption in ecology. Second, the transitivity of a competitive hierarchical network is examined using data from the same experiment with A. thaliana. We show that intransitivity is a structural component of the competitive networks here because there were no true dominants, patterns of dominance changed with nutrient levels, and there were competitive reversals. We determined the relationship between the frequency of reversals, competitive equivalence and the length of reversals, each with respect to accession diversity. We find that all of these intransitive characters increased with accession diversity. This result has implications for coexistence based on current theoretical models of intransitivity. Third, we quantify the cost of a plant defense in an experiment with Mimosa pudica L. using a unique leaf touching device. Mimosa pudica is a plant that defensively closes its leaves when triggered by touch. There is a trade-off to this behaviour as there are increased energetic costs and photosynthetic opportunity costs with greater frequency of leaf closing. With the leaf touching machine, we found that touch itself stimulated growth. However, comparing daytime touching that stimulated leaf closure to nighttime touching that did not stimulate leaf closure, we find that there were costs in reproductive allocation attributable to the frequency of leaf closure. These results contribute to a growing documentation of the cost component of plant defensive strategies. Fourth, we fill some of the gaps in our knowledge in the behavior of M. pudica by measuring the effects of competition, nutrients and rhizobia on leaf re-opening behaviour over a 9 month period. We found that each of the treatments had an effect on plant size, but competition alone had an effect on inflorescence production. In the presence of a competitor, and as plant size increased, leaflets of M. pudica took longer to re-open upon stimulated closure. This adds to a catalogue of complex behavioural responses in M. pudica that has garnered the attention a broad spectrum of behaviourists. Lastly, we present a new method using digital image correlation (DIC) to characterize plant root traits, traits that are generally difficult to observe. This method is novel because we use the measurement and analysis of soil to infer the movement and position of roots. We demonstrate the effectiveness of this method in characterizing the static and dynamic traits of Helianthus annuus L. roots. This application of DIC promises to be an effective, time-efficient, cost-efficient and likely scaleable approach to studying roots.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.