The assembly of plant communities in relation to overlap in mycorrhizal and pathogenic root fungi

Plant species commonly associate with symbiotic arbuscular mycorrhizal (AM) and pathogenic root fungi, with many plants overlapping in their fungal community compositions. Overlap in AM fungi could promote coexistence by favouring competitively inferior or rare plants, or through the establishment of common mycorrhizal networks. Coexistence could also, however, be impeded if shared AM fungi disproportionately benefit competitively superior or abundant plant species. Overlap in pathogenic root fungi among closely growing plant species should increase the likelihood that an uninfected plant becomes infected, leading to reduced coexistence. Using vegetation plot data from an old-field plant community along with high-throughput sequence data on AM and pathogenic root fungal associations, we conducted three specific evaluations. First, we used null models to determine whether estimated overlap in AM or pathogenic root fungi among coexisting plant species was higher or lower than expected by chance. Second, we assessed whether estimated overlap in AM and pathogenic fungi differed between positively co-occurring and negatively co-occurring plant species. Third, we examined whether variation in plot-level plant species richness was explained by the degree of estimated overlap in AM and pathogenic root fungi among those species. We found no evidence that estimated overlap in AM or pathogenic root fungal communities was higher or lower than expected under our null model. Additionally, positively and negatively co-occurring pairs of plant species did not differ in their estimated overlap in either group of fungi. However, plant species richness was significantly higher in plots where plants were estimated to overlap more in AM fungi and significantly lower in plots where plant species were estimated to overlap more in pathogenic root fungi. Our results suggest that overlap in root fungal associations among plant species appears to be predictive of plant species richness, and therefore the assembly of plant communities.Read the free Plain Language Summary for this article on the Journal blog.