An experimental test of the functioning of arbuscular mycorrhizal symbioses across scale
J. KLIRONOMOS (1). (1) University of British Columbia Okanagan, Kelowna, BC, Canada
A major goal in mycorrhizal ecology is to better understand the factors that determine plant growth response to mycorrhizal fungi. Most studies have focused at the individual plant level using +/- mycorrhizal treatments under greenhouse settings, with response outcomes ranging from parasitism to mutualism. Often the direction and magnitude of these outcomes are unpredictable. Here I will present data from two experiments conducted at different scales (one at the local level, and the other at the biome level), which are designed to better understand how environmental variables influence plant growth response. Locally, by conducting plant growth response experiments along environmental gradients (soil nutrients, pH, and moisture) it is clear that plants respond to mycorrhizal fungi differently. Under optimal conditions, the outcome of the symbiosis is parasitism. However, under more stressful conditions, the outcome is mutualism. This indicates that the mycorrhizal symbiosis may best be regarded (from a phytocentric viewpoint) as an insurance policy. At the biome level, we find similar trends. Plant growth response to mycorrhizal fungi differs across ecosystem types, with stronger positive responses in more extreme conditions, especially in arid and semi-arid ecosystems. Collectively, these results give us a more predictable understanding of mycorrhizal functioning in a variable environment.
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