Population-level specificity in the plant-mycorrhizae association alters intraspecific interactions among neighboring plants.

Although variation in the effectiveness of the plant-mycorrhizal association has been demonstrated among plant species and among crop cultivars, the level of specificity of the plant-mycorrhizal association in natural populations and, in particular, its effect on intraspecific plant interactions have not been explored. To examine the influence of the specificity of the plant-mycorrhizal association on intraspecific interactions in Allium vineale, we surrounded target plants with either genetically identical neighbors, neighbors from the same population, or neighbors from a different population, and planted them in pots either with or without a soil fungi community. Overall, the presence of a soil fungal community was beneficial for plant growth, and thus the soil fungal community effects in this system are dominated by the mutualistic effect of mycorrhizae. In addition, both the target plant and neighbor plants had a relatively greater benefit from the mycorrhizal association if the neighbors were genetically identical or from the same population than if the neighbors came from a different population. Thus, there is specificity in the interaction between A. vineale plants and the soil fungal community at the population level, and this specificity favors intraspecific interactions among plants from the same population. In addition, in the presence of the soil fungal community, the variance in plant size within a pot was greater among neighbors from a different population. Therefore the growth advantage for plants growing with neighbors from the same population was not due to pre-emption of resources by individual plants. This finding provides indirect evidence to support the hypothesis that plants from the same population were able to share a more efficient hyphal network.