PARENT SESSION
Contributed Oral Session 26: Soil Fungi
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal

Interactive effects of arbuscular mycorrhizal fungi and water table on experimental wetland plant communities.

Wolfe, Benjamin^*,1, Weishampel, Peter², Klironomos, John¹, ¹ University of Guelph, Guelph, ON, Canada² University of Minnesota, St. Paul, MN

ABSTRACT- Arbuscular mycorrhizal (AM) fungi have been shown to influence diversity and productivity in many different types of plant communities, but the role of local abiotic soil factors in mediating these community-level effects is unknown. We manipulated the presence of AM fungi (+/-) and water table depth (high: at the soil surface; low: 8cm below soil surface) in mesocosms designed to simulate patches of species-rich calcareous fen plant communities where the dominant plant species are non-mycorrhizal (Carex sp.) and subordinate species are mycorrhizal. Total aboveground community biomass increased with AM fungi present in the low water table environment, but decreased with AM fungi present in the high water table treatment. In both water table treatments, the presence of AM fungi decreased plant diversity, but this effect was stronger in the high water table treatment. The proportional abundance of subordinate plant species did not change in the presence of AM fungi in the low water table treatment, but significantly decreased in the high water table treatment when AM fungi were present. AM fungal community composition, assessed by terminal restriction fragment length polymorphism of 18S ribosomal DNA, shifted to low diversity communities dominated by one or two ribotypes in the high water table mesocosms, which may explain the change in AM fungal function from positive to negative in the low versus high water table treatments. Given that water table depth in calcareous fens is spatially heterogeneous at small scales due to bryophyte hummocks, interactions between water table and AM fungi could lead to spatial variation in plant community composition.

Key words: mycorrhizal fungi, wetland, mutualism, t-RFLP