The Effect of Local Adaptation on Mycorrhizal Fungi-host Relationships

Background/Question/Methods The successful establishment of a species in a new environment is a result of the complex interaction of genetic, biotic and abiotic factors. Local adaptation, defined as the differential success of genotypes in their native environment relative to a foreign environment, may be one mechanism by which genetic diversity can be maintained within a species; however, it may also lead to divergence of populations and possibly even lead to speciation. Mycorrhizal fungi form symbiotic relationships with 80% of terrestrial plants. These relationships are characterized by the exchange of soil nutrients for carbon from the host. These fungi have been shown to affect essential host traits associated with biotic and to alter competitive interactions within and among plant species. Given the ubiquitous nature of mycorrhizal associations, studies examining plant local adaptation that do not take into account this essential interaction may be missing an important factor in the ability of a plant population to adapt to the environment. Using meta-analysis on a data set comprised of 1591 studies (from 178 papers), we explored the role local adaptation—as determined by relative geographic origin of the plant, fungi, and soil—plays in altering plant response to mycorrhizal fungi. Results/Conclusions Regardless of whether plant, fungus, and/or soil originate in sympatry (same origin) or in allopatry (different origin), the mean effect size of mycorrhizal inoculum on host biomass was positive, emphasizing the mutualistic nature of mycorrhizal fungi relationships. The effect was larger when the plant and fungus originated in sympatry compared to allopatry. Similarly, the effect of mycorrhizal inoculum on host biomass was also larger when the plant and soil originated in sympatry. There was no significant effect of fungal-soil relative origin on effect size. Overall, these results indicate that the effect of mycorrhizal inoculum is positive, but that plant adaptation to local soils and mycorrhizal fungi plays a significant role in altering this effect. While further analyses which account for other sources of variation in experimental outcomes may provide more precise estimates of the importance of local adaptation in mycorrhizal interactions, future experiments considering mycorrhizal fungal relationships should take into account the relative geographic origin of mycorrhiza and the soil used in their experiments