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
Hierarchies of plant-plant and plant-fungal interaction strengths with varied resource ratios.
Freund, Deborah1, Miller, Kathye1, Lee, Tali1, Weiher, Evan1, 1 University of Wisconsin-Eau Claire, Eau Claire, WI, USA
ABSTRACT- Ecologists have long recognized the important roles of competition and mutualism in shaping plant communities. We sought to investigate a series of related questions regarding the nature of positive and negative interactions by conducting a two-year factorial experiment in which we grew 6 prairie plant species (three C4 grasses, three forbs, stratified by size) with and without neighbors, with and without high dosages of chlorothalonil fungicide (which reduced average MF colonization by 34% - 43%), and with varied resource ratios (control, 15 g N m-2 ammonium nitrate fertilizer, 15 g m-2 N as balanced complete fertilizer). Plant-plant interactions were mainly negative and plant-fungal interactions were mainly positive, but not always. Hierarchies of plant-plant interaction intensities were concordant among the species (W = .77, p < .001), which means the strongest competitors tended to remain the strongest, regardless of treatment. There was a weak, but significant concordance of treatments (W = .42 p = .040), which means there was a weak tendency for species to perceive the strongest competition intensities in the same treatments. Nutrient additions reduced competition intensity. The best competitor benefited from neighbors, and it was a medium-sized forb. Hierarchies of plant-fungal interaction intensities were not concordant among either the species (W = .35, p = .229) or the treatments (W = .064, p = .858), so there was no tendency for plant-fungal interaction strength to be stronger in some treatment combinations than in others, nor did the species have strongly consistent relative responses to fungi. Even so, there was a marginal correlation between ability to interact with plant neighbors and ability to interact with fungi (r = .667). The next steps include assessing the role of MF colonization rate on biomass and competitive ability. These results support different aspects of both the Grime/Keddy camp and the Tilman camp regarding the nature of competition and they support Hartnett/Klironomos ideas that plant-fungal interactions may be both context-dependent and idiosyncratic.
Key words: competition, mycorrhizal, symbiosis, interaction