Home-field Advantage. Does the Geographic Origin of Plants, Mycorrhizal Fungi and Soil Determine Plant Responses to Mycorrhizal Symbioses?

Higher fitness of genotypes in their native environment relative to a foreign environment, or local adaptation, can drive the maintenance of genetic diversity in a species, and can also lead to population divergence and even speciation. Mycorrhizal fungi can play an important role in mediating a plant’s interaction with the local abiotic and biotic environment. Therefore, studies examining local adaptation of plants that do not take mycorrhizal fungi into account may be missing an important factor in the ability of a plant population to adapt to the environment. Using meta-analysis on a dataset comprising 1,659 studies (from 183 papers), we explored whether the geographic origin of the plant, mycorrhizal inoculum, and/or soil influenced plant biomass response to mycorrhizal fungi. Regardless of whether plant, fungus, and/ or soil originated in sympatry or allopatry, the mean effect size of mycorrhizal inoculum on host biomass was positive. The effect was larger when plant and soil origin were sympatric but allopatric to the fungus, or when plant and fungus origin were sympatric but allopatric to the soil. However, the statistical significance of these trends was marginal. Overall, these results strongly support mutualism in the mycorrhizal symbiosis, but provide little support that the relative geographic origin of plants, fungi and soil alters the nature of the interaction. This lack of support may be an artifact of our study, which is limited in two ways. First, our study defined ‘local’ relative to geographic distance, assuming it would be correlated with ecological distance. Second, while these analyses represent one of the most comprehensive meta-analyses to date, we were greatly limited by the number of papers that reported origin of the soil, fungi, or plant. As such, this meta-analysis provides a first brushstroke to address the impact of local adaptation on mycorrhizal relationships.