Armstrong, Joseph E. , Borowicz, Victoria .
Ecology of a hemiparasite in a prairie community.
Hemiparasites interact with host plants on two trophic levels. While extracting water and nutrients from hosts they compete with them for these resources and for light. Based on observations of Pedicularis canadensis from two sites, we hypothesize that this hemiparasite is a strong parasite but a weak competitor, and so its impact on a community is context dependent: the hemiparasite exerts its effect through parasitism when competition for light is reduced. We predict that P. canadensis, a short perennial growing in a restored tallgrass prairie, will reduce productivity most under low nutrient conditions where vegetation is thin and light levels are consequently high, and least under high nutrient conditions where lush vegetation shades the hemiparasite and impedes photosynthesis and transpiration. To test this hypothesis we initiated a multi-year experiment in which 1 square meter quadrats were given one of eight treatments that were combinations of three factors: hemiparasite removal (or sham disturbance), mineral nutrient enhancement, or shade. The dry mass of hemiparasite, grasses, and forbs from the center of each plot was determined after one growing season. Nutrient enhancement nearly tripled grass biomass and doubled forb biomass on this poor-soil study site. Removal of the hemiparasite increased grass and forb biomass a little and this increase was most pronounced in unshaded plots where competition for light was low. Shade had minimal impact on host plants but decreased P. canadensis, especially in fertilized plots. We are encouraged by these early results, so the treatments will be continued.
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1 - Illinois State University, Department of Biological Sciences, Campus Box 4120, Normal, Illinois, 61790-4120, USA
2 - Illinois State University, Department of Biological Sciences, Campus Box 4120, Normal, IL, 61790-4120, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Lake Ontario/Hilton
Date: Monday, July 9th, 2007
Time: 11:15 AM