PARENT SESSION
Oral Session # 99: Late-Breaking Newsworthy Presentations.
Presiding: E Preisser and G Larocque
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 205.
Does diversity mediate frequency-dependence in plant communities?
Schnitzer, Stefan*,1, 3, Kinkel, Linda2, Xiao, Kun2, Reich, Peter3, 1 University of Wisconsin - Milwaukee, Milwaukee, WI, USA3 University of Minnesota, St. Paul, MN, USA2 University of Minnesota, St. Paul, MN, USA
ABSTRACT- Negative frequency-dependence has been proposed as a mechanism that maintains plant community composition and diversity. If negative frequency-dependence is mediated through soil-borne pathogens, then the health and performance of plants may be determined by the number of species in the community. Specifically, as plant diversity increases, the density of species-specific pathogens will decrease for any given species because that species will occupy a smaller proportion of the soil. In low diversity communities, however, the soil pathogen load should be relatively high for all of the species, assuming that plant densities are similar to high-diversity communities, because each species will occupy a relatively large proportion of the soil, resulting in poorer performance for all individuals. We tested the hypotheses that: 1) negative frequency-dependence via soil pathogens will reduce plant performance for plants grown in soil taken from conspecific monocultures compared to interspecific monocultures; and 2) higher species diversity will mediate frequency-dependence, resulting in lower rates of infection by pathogens and thus greater plant health. To test the first hypothesis, we used a greenhouse study where we planted seeds of six target species of native grassland plants in pots with soil from experimental plant monocultures in which they were present (home treatment) and not present (away treatment). To test the second hypothesis, we planted the same six target species in home and away treatments, but used soil from both monoculture and 16-species plant communities. After several months of growth in a greenhouse, we quantified the amount of root disease as well as the total dry biomass for each plant. Disease severity was generally higher and plant biomass lower in the home than away soils, supporting hypothesis 1, though this varied among plant species. Likewise, disease severity was higher and plant biomass significantly lower in the high- versus low-diversity soils, supporting hypothesis 2.
Key words: density-dependence, frequency-dependence, diversity, pathogens