PARENT SESSION
Poster Session 38: Mutualism / Parasitism
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Negative effects of soil biota on Andropogon gerardii.

Markham, John¹, ¹ Botany Department, Winnipeg, MB, Canada

ABSTRACT- Andropogon gerardii is the predominant and competitively dominant plant of the tallgrass prairie. In a remnant community at the northern limit of the tallgrass prairie A. gerardii was found to be the dominant grass forming large patches. These patches had reduced cover near their center. A. gerardii seedlings were transplanted into pots inoculated with a small quantity of soil from plant patches dominated by one of four different plant species from the tallgrass community: A. gerardii, Panicum virgatum, Solidago canadensis or Spartina pectinata and grown for 16 weeks either with or without the addition of Benomyl to reduce mycorrhizal infection. Soil inoculation significantly reduced growth and reproduction. Plants receiving no soil inoculation were an average of 3.6 times larger and 4.4 times more likely to have produced inflorescences than plants inoculated with soil from the field. Soil inoculated plants were colonized by both AM fungi and a parasitic oomycete fungus. Plants inoculated with soil from A. gerardii patches had the lowest shoot mass and were more likely to be infected by the parasitic fungi. Significantly more plants inoculated with soil from A. gerardii patches had AM mycorrhizae and plants that were mycorrhizal had significantly smaller shoot masses than non mycorrhizal plants. Benomyl application decreased plant growth, had no effect on the probability of plants becoming mycorrhizal but increased the probability that they would be infected by the parasitic fungi. The negative effect of the soil biota on A. gerardii may help to maintain diversity in this tallgrass prairie community.

Key words: Andropogon gerardii, negative feedback, parasitic fungi, tallgrass prairie