The effects of defoliation on growth, reproduction and pollination of a non-native legume (Astragalus cicer) in the mixedgrass prairie

  • Author / Creator
    Phung, Angela M
  • Herbivory can lead to trade-offs between plant growth and reproduction as defoliated plants lose initial resource investments and have reduced photosynthetic capacity. This trade-off can lead to reduced investment into reproductive structures and have repercussions for floral traits, pollinator attraction and plant reproduction. I investigated the effect of timing and intensity of artificial herbivory on the growth, floral traits, pollinator visitation and reproduction of an exotic perennial legume, Astragalus cicer L. My study was conducted in a native mixedgrass prairie grazed by cattle. Over two summers, I clipped plants and measured the production of inflorescences, pollinator visitation, and production of vegetative and fruit biomass to evaluate the impact of low or high intensity clipping either earlier or later in the growing season. In 2015, I additionally measured nectar production to better understand the effect of clipping on floral components.In my first study, I found that high intensity clipping led to smaller plant spread, but leaf biomass did not differ among treatments, and in 2014, high intensity clipping produced more stem growth compared to low intensity treatment. Late-high intensity clipping also produced more vegetative biomass in 2015 compared to 2014. In 2014, late-high intensity clipping treatments led to lower fruit biomass and late clipping treatments led to a lower fruit to vegetative biomass ratio. My results demonstrate that Astragalus cicer L. is able to withstand a higher clipping intensity with limited impacts on vegetative growth. Further, when plants are clipped earlier, prior to flowering, there is minimal impact to reproduction. In my second study, I found that late-high intensity clipping led to fewer numbers of inflorescences, while a late clipping intensity negatively affected nectar sugar per flower, fruit and seed production. However, treatments had a minimal effect on pollinator visitation. Aside from effects on nectar production, effects on number of inflorescences and reproduction were mostly limited to 2014. Since treatments had minimal effects on pollinator visitation in 2014, the effect of clipping on plant reproduction may have been due to changes in resource availability rather than reductions in pollinator visitation.Despite recurrent herbivory by cattle, the ability of clipped Astragalus cicer L. to produce similar amounts of vegetative biomass to unclipped plants may help to explain its abundance and success in the native grassland I studied. However, late grazing during flower development can negatively affect floral resources available to pollinators and plant reproduction, and can potentially lead to consequences for long-term fitness of Astragalus cicer L.

  • Subjects / Keywords
  • Graduation date
    Spring 2017
  • Type of Item
  • Degree
    Master of Science
  • 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.