Borowicz, Victoria , Armstrong, Joseph E. .
Resource limitation and the impact of a hemiparasite on a restored prairie.
Hemiparasitic plants are photosynthetic but acquire some water and minerals from nearby plants through root haustoria. Consequently, hemiparasites may simultaneously compete with and parasitize neighboring plants. Based on observations of Pedicularis canadensis from two prairie sites, we hypothesized that this hemiparasite is a strong parasite but a weak competitor for light, and so its impact on a community would be a function of resource supply: the hemiparasite exerts its effect through parasitism most strongly when light is abundant and soil nutrients are limiting. We predicted: (1) that parasitism by P. canadensis, a short perennial growing in a restored tallgrass prairie, would reduce community productivity; (2) this reduction would be greatest 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 its growth; and (3) functional groups of species would differ in response to parasitism. To test this hypothesis we conducted a three-year experiment in which 1 m2 quadrats were given one of eight treatments that were combinations of three factors: hemiparasite removal, fertilizer addition, or light reduction (shade). The dry masses of hemiparasites, grasses, legumes, and remaining forbs from the center of each plot were determined after the third growing season. Removal of the hemiparasite, addition of fertilizer, and full sun significantly increased productivity but the impact of P. canadensis was independent of resource level. Removal of P. canadensis most strongly affected grasses and had little impact on legumes. Forbs showed the largest response to fertilizer and the least response to shading. Surprisingly, we did not detect a significant response of the hemiparasite to fertilizer and light manipulation. However, site heterogeneity probably swamped effects of treatments. These results fall short of explaining our initial observations.
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1 - Illinois State Unversity, School of Biological Sciences, Campus Box 4120, Behavior, Ecology, Evolution, and Systematics, Normal, IL, 61790-4120, USA
2 - Illinois State University, School of Biological Sciences, Campus Box 4120, Behavior, Ecology, Evolution, and Systematics, Normal, IL, 61790-4120, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Alpine B/Snowbird Center
Date: Tuesday, July 28th, 2009
Time: 10:30 AM