Joseph E. Armstrong

Research on Hemiparasitic Plants and their impact on prairie community organization


karens.jpg (86023 bytes) Red-headed undergraduates, Karen & Karen, on their prairie study site with tools of the trade.

Parasites and their hosts have been one of  the least studied interactions from an ecological/evolutionary perspective, and, in particular, their impact on community organization.  Pedicularis (Orobanchaceae, formerly Scrophulariaceae: Rhinanthoideae) are hemiparastic plants. Pedicularis canadensis (click to see a picture), whose common names are lousewort or wood betony, is an obligate root parasite on a wide range of host species, but it retains its photosynthetic ability. Reproduction and host foraging are accomplished both sexually (seeds) and asexually (rhizomes). Pedicularis appears to exert a considerable influence on prairie height and host reproduction. This parasitic plant forms oval patches that are spreading unidirectionally (click here to see a field picture) into unparasitized areas at a remarkable rate. This work centers on several questions. Does Pedicularis demonstrate foraging behavior and actively select preferred host species? Does Pedicularis obtain the most benefit from preferred host species? How does nitrogen availability affect the plant host-hemiparasitic plant interaction and community organization?  The hemiparasite's benefits from both photosynthesis and parasitism should be maximized under conditions of low nutrient availability, whereas, when nutrients are not limiting, the benefits obtained from photosynthesis and parasitism are both reduced.   Click here to see a PowerPoint presentation about this work.

Hemiparasitic plants prey on and compete with other green plants. Their parasitism may alter the competitive interactions, e.g., by reducing the prairie canopy height and reducing shading. A long-term research program is being constructed in collaboration with my colleague Victoria Borowicz.

Here is the link to more information about research on parasitic plants.

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